First off, you should be getting Stim before Concussive, I'll explain why in a second.
The Marauder is both a vastly overrated and underrated unit. It has pitiful dps (against anything that isn't armored) and largely exists as a meat shield for the much higher dps, much lower hp, Marines. The ideal Marine/Marauder ball is relying on Marauders to tank while Marines dish the damage. Let's take a closer look at the Marauder:
125 HP
1 Armor
10+10 damage (or 6.67+6.67 dps)
Against your average Zealot that 1 armor is going to cost him ~15% of his damage, while the much more cost effective Marines dps him down. Additionally, any Stalkers only do 70% as much dps (as the Marauder).
So Marine/Marauder is already set up nicely against Zealot/Stalker, which brings me to Stim. Marines, being your real dps here, really need Stim to help take out the slower Protoss units and it also gives them the ability to kite. Compared to that Concussive Shell is just icing. In fact, you'll see a lot of Terran (like Jinro) move out just as Stim finishes and Concussive starts, because they want to maximize the timing window Stim represents (and because Concussive's shorter build time often means it'll finish just as they start engaging).
Now you asked about earlier pushes than Stim, and the list is very short:
Both of these plays fail against a 1 basing Protoss player. The truth is, Stim is very early, and very powerful, you're not going to find anything better before it. If you're consistently losing a Marauder heavy ball while dealing early pressure, then I suggest you reexamine your composition. Most 3 Rax play has an even amount of Marauders and Marines. Earlier pushes (like 2 Rax), tend to be very Marine heavy, with a few Marauders thrown in to act as meat shields.
I hope this helps
Weakness/Winning Counter: Short Answer Helions (w/BlueFlame) and Banshees.
A counter build like this was featured the other day on Day9 dailies (#258). He has an excellent video up interviewing the guy who perfected this TvT counter build. The build is fairly technical but doesn't require exceptional APM with its weakness possibly being Thors.
Summary: Helions roar in devastate the marines, and Banshees cleanup the Tanks as Helions retreat. This build only requires 2Port 2Fact for a long time, reducing the need for other production buildings. It seems a key to this build you should maintain air superiority.
Basic build goes something like this (Taken from iEchoic's post):
- 10 supply
- 12 rax
- 13 ref
- 15 OC
- 15 make one marine, then queue another (only make 2 marines)
- 16 supply
- 17 ref
- (supply counts discontinued from here keep making scvs nonstop)
- factory
- factory
- tech lab on rax
- swap first factory onto rax
- make 1 hellion & get preigniter
- make 1 hellion on second factory
- clear xelnagas with hellion
- starport
- starport
- supply drop (see faq)
- medivac
- poke up ramp with a hellion, try to scout composition
- build order discontinued here, starport production is dependent on opponent's composition
iEchoic's excellent forum post.
http://www.teamliquid.net/forum/viewmessage.php?topic_id=189624
Best Answer
Wall in, tech up to siege tanks w/ siege, build a few, and plant them at your base entrance. Assuming you scout early enough, this method requires the least micro and will allow you a solid transition into an expansion.
You can also try to build up a few bunkers & stock them with marine/marauder. This can be effective as well as long as you keep the ranged Protoss units out of range of your repairing SCVs (a.k.a. walling in).
For either of the above, you'll want to watch out for void rays. That's usually how your 4-gate counter will be countered.
Banshees with cloak can be somewhat effective but the siege tanks have more longevity in terms of utilization for the rest of the match.
Marauders with concussive shells can also be effective if you have the micro for it.