A couple problems with the span calculation, IMHO (I am not a Licensed Professional Engineer):
Select structural (the lumber grade) is frequently impossible to come by at an ordinary lumberyard, will cost the earth if it can be had, and is even less available (AFAIK) in pressure treated (though you should not need that, as per comments.)
Number 2 is generally the grade you should design for unless you are sure you have a source for a better grade and can stand the price of it... You can get the same loading from 2x8 number 2 on 19.2" centers (5 per 8 feet - there's a symbol on most modern tape measures for that spacing) as your select structural on 24". Or you can get significantly more load (or span) from 2x10 number 2 on 24" centers
The position of this roof on the sidewall of a house (if it's "like the picture") may cause the buildup of a snowdrift on the roof - that needs to be allowed for if the 30 lb snow load is anything other than mythical (ie, I think that snow load is the code standard minimum, so it is often in code where snow is never expected....)
You have not stated any reason that would appear to prevent the obvious solution (if you consider it a problem at all) of running the network wiring along the face of the wall at the same level as the server rack, or roughly 12" below the power conduit. If the basement/crawlspace floods enough to flood the server rack you probably should rethink the location of the server rack, and in any case the cables being run horizontally higher up won't help a bit in that case.
You could also move the cables far enough forward into the room (3-4 feet, say) that they don't encroach on your shelving unit, then run them back along the joist (it's holding up a floor above if it's a crawlspace, so rafter is not the right term - those have a roof above them) to the server rack.
Despite a number of "trying to be perfectionist" scare stories about needing to keep network and power cables well-separated, the fact is that the differential pairs in Cat5 (or 6, or 7) are designed to reject interference, and that the frequency domains of networking signals and power line noise are utterly different. So, in practical terms you can wire tie (just not too tight - sharp bends are bad) the network wires to the power conduit and not have any interference problems in a typical home application.
Coaxial cable is self-sheilded by design and thus also highly unlikely to pick up any objectionable interference simply by being run next to power or network wires.
Since all you are really considering is running them parallel at a few inches distance, you will be fine doing that (do avoid a sharp bend anywhere, particularly where you turn downwards and might be tempted to yank the wire tight around the J-hook.)
While I do generally try to maintain the oft-suggested 12" separation for parallel runs when designing from the ground up, I have hundreds of feet of Cat5e that is in close proximity to power wiring in old building retrofits, and connected to switches that report error rates - and those error rates are pretty much always zero, unless there is a more fundamental problem with the cable (like rats chewing on it, a sharp kink/bend, or a bad connection at the end of it.)
Best Answer
You should be fine if you're just a tiny bit careful.
You should not notch these, but careful drilling should be perfectly fine.
It's totally okay, for example, to trim the ends off of these--they aren't supporting the roof load, only supporting the overhang itself. (drilling through the trusses on the inside is another matter entirely!)
My first thought was I'd use a bit just large enough to poke the Cat5e cable through, drill exactly in the center of the top chord (the "beam") about 2/3 of the way back from the end.
In general, you don't want to drill too close to the ends of a beam (or you run the risk of it splitting). If you're only drilling a 1/8th (or so) inch hole, back away from the edge, I can't imagine this being a problem.
Or drill two small holes or one slightly larger one and pull 2 cables.
But why not consider using conduit, just for a bit of future proofing? Maybe you decide you want to pull an HDMI cable six months from now, or something else?
Hardly anybody used conduit when they pulled co-ax cable through their walls a couple of decades ago, and now you'd much rather have HDMI running through the walls. With conduit, pulling different or additional cable would be a much easier task.
You could just pull 1/2" or 3/4" EMT, or maybe you could even get away with 1" (3/4" might be just big enough to pull something with pre-attached ends like HDMI). EMT would be the most stable option.
You could run a raceway under the eave, but if it's plastic you might really be surprised at the amount of thermal expansion and contraction it will undergo as the seasons change, and you could end up with it warped and pulling away from the wall.
I would avoid the grey PVC electrical conduit because it expands and contracts to an extent you wouldn't believe and you have to use expansion couplings and leave everything loose enough (bigger holes) that it doesn't bind.
Another option might be ribbed flexible low-voltage PVC conduit (it'll typically be orange or blue).
But the more I think about it, I'd just use 1/2" or 3/4" metal conduit.
You obviously want to pull at least Cat5e, but you might consider pulling Cat6A or even Cat7 just to be future-proof. Cat5e is fine for Gigabit Ethernet (up to 125 Megabytes per second in both directions simultaneously). Cat6A will definitely support 10Gbps Ethernet (over a Gigabyte per second), and presumably future Ethernet enhancements will be able to push even more over Cat7. Cat 6A and Cat 7 are harder to terminate, with all the shielding and the heavier jacket, but you're not talking about doing very many terminations.
What I'm really getting at is that without pulling any additional cables, especially if you pull 2 now, you can use the cable you pull as a trunk link between two Ethernet switches to transparently connect your whole house into one network, and in a home setting you will never suffer any performance problems doing that.
As far as drilling these rafter ends: If you think about a steel I beam, virtually all of the load is carried in the top and bottom plates of the beam, and the material between the plates just serves to keep them apart from each other. That's why the I beam can have all the material removed from both sides instead of being one massive solid beam. In fact the massive beam would be weaker because the top and bottom surfaces aren't really any stronger than in an I beam, but the beam would have to support many times the weight just to hold itself up.
There's less load in that vertical section of the beam the further you get from the edges, and virtually no load in the dead center. Manufactured floor joists operate on the same principle and that's why you'll see surprisingly large holes cut in the middle of those joists without it affecting the integrity of the floor (presuming the holes aren't drilled too close to the ends).
If you cut a notch in the top or bottom plate of the joist, on the other hand, you've compromised it, or ruined it. In the case of manufactured trusses and joists, the manufacturer will have very specific instructions on where you can drill, how big, how many holes, how far apart they have to be, etc.
But here, you're talking about the overhang. The structural load of the roof is resting on the wall and you could cut most of that overhang off without affecting it.