It's difficult to model the situation with rational analysis, there's too many intangible factors. You could do an empirical test. You need to support 20 lbs per fastener. We can apply a safety factor of 3 for ultimate strength, so the fastener should support 60 lbs without actually breaking. So you would need 2-4 fasteners to support your weight. Round down to the closest whole number. Install the clips as you did in the wall, except now install a metal strap between the screw head and clip. Arrange the straps so you can step into them to weight the system. Arrange the straps such that your weight is distributed evenly to each fastener.
Weight the system and see if they break. If you live in a seismic area, bounce on them a bit and see if they break. You'll either be able to sleep better or you'll know what to do next, depending on the outcome. Obviously there are better ways to set up an empirical test, I chose to illustrate a quick and dirty method just as an example. Be sure you are protected from flying shards of metal.
Regarding an increaser for the number of fasteners. No, you can't do that. It is a valid concept though, for example you can use a higher allowable bending stress in multiple floor joists than you can in a single use situation such as a header. The concept is not generally applied to fasteners.
Response to OP's Update
Shear strength in relation to fasteners partly depends on what the fastener is holding. In this case it's known as a metal side plate condition, meaning the expected failure mode will either be the top of the screw failing through the shank (shear) or the wood collapsing under the compression from the screw. It's rare in reality to have a perfect shear condition, there is usually some bending and tension components as well.
A true shear condition would something like a metal strap screwed to the wood surface and all the force was parallel to the wood surface, exactly perpendicular to the screw shank. In your test, you mostly have the vertical shear component, but there is a tension component as the center of mass is away from the wall surface. We can safely ignore the tension component in calculating a working load since 80# in pure shear is more conservative than 80# shear and, oh... say 15# tension combined.
A picture of the clip was helpful, I imagined a much worse condition. Either way, the ultimate strength will not be proportional to shear alone, there are other factors difficult to model, thus testing is the best approach. The failure mode you experienced is a bending failure, but your actual installation, while having a bending component, is in fact mostly a shear condition.
The duration of load is a factor. The usual allowable stresses specified in construction are for permanently applied loads. The allowable stresses can be increased for shorter durations, 15% for a few months, 25% for a few weeks, 33% for a few minutes. Meaning we should reduce the allowable load determined through short term tests accordingly. But we also don't know the ultimate load since you didn't achieve failure. Just as well, uncontrolled destructive testing can be a little too exciting. You also haven't run multiple tests (I assume) to confirm you are getting consistent results.
Let's say you did run multiple tests and they all actually failed at 80#. When you apply the 3x safety factor, then adjust for duration of load, you end up with a working load of 20#, exactly what you need. Considering there was no failure experienced, and the installation does appear to be predominantly shear, I think your installation is safe. Barely. Next time around, use heavy ordinary wood screws ;)
I have to say that I am no fan of cordless framer nailers. I have had two different ones, a Porter Cable and a Pasload. Both were gas fired. The PC was a disaster. Had lots of problems with the propane cells seating properly and nails jamming. Got the Pasload, worked OK, but slow and the smell was so bad that I only used it outdoors. The gas cells are expensive also. After two days on a job, I went back to my trusty Bostich 88 and ran the compressor off a gen set. The other thing I hated was that it could not shoot 10d wire collated nails that I use in my other air framers. Those plastic bits flying at your face sting and you have to reload much more often. Absolutely hate plastic collated nails!
To be honest, I have not tried one of the new battery operated models yet. For framing, I like the largest, thickest nail.(3 1/4") and most cordless ones don't shoot the same larger nails I use in my Bostich.
Since your projects are at home and you already have a 135# compressor, I really think you will get a lot more nailer for the $$$ if you stick with a Bostich 88 mag or similar. You will be able to shoot 4d to 10d nails. The unit itself is much lighter, cheaper and very dependable.
For what you pay for a good cordless, you could own a good framer, 16ga finish and 18ga brad gun, thus having the right tool for every nailing job.
I have to say however, a good cordless finish gun is wicked handy and the battery models have plenty of power, but this humble carpenter is not sold on cordless framers.
Best Answer
With that many I would probably use nails in my gun. If you don’t have a gun but do have an impact driver I would use screws , this would be the last time I used that guy , yes there are structural screws I like fasten master torx head, these have a long smooth shank with the threads on the bottom 1/2 maybe slightly less on 3”.