I'm still very very satisfied by how well a C2 game can run, even on old hardware.
My game runs very smoothly even on crappy laptops now, I'm impressed.
You definitely can push hard on C2, and have tons of ressources with no problem. It does a superb job at managing/optimizing the memory for you.
As jobel mentioned it, I had some problems with people wanting to stream some Penelope footage.
Half of these problems were only because of me (you would want to have a look at "delta time" management way more closely than I did) as I didn't test enough my game in extreme conditions (under 15fps or at more than 100fps on top end monitors).
The other half is how the frameskip is handled in C2. 40fps doesn't look like 40fps but sometimes feel more like 20, and when people stream the game in bad conditions (play+local record+ online stream on poor setup) it shoes. For normal use, aka only play the game at 60fps on many many machines, you can be sure it will compare very well with games made using Unity or GM. Again, even 2 years later, I'm still happily surprised by the C2 perfs.
Honestly, if you're not interested in consoles (<be really sure of this, all consoles), I don't see why you shouldn't pick C2 for your game. No engine is perfect, and this one is very good, very fast, very cheap and have a GUI designed by a brilliant mind. Wish you the best with your game!
Coming from Aurel, this is all you guys need regarding C2 and "Big Games" for PCs.
In my limited experience, it works just fine baring some fixable issues (Node Webkit relying on Chromium which Google messed up for a few versions). But these are fixable issues, yes, it requires a bit of troubleshooting.
ps. C2 for PC/MAC has excellent memory handling of large amounts of sprite & art assets.