Hi Firelord, first of all a small comaprsion between FPSC and C4 (I`ve been working on both of them):
In terms of ACHIEVABLE gfx quality, the two are almost on par, with C4 being better by nuances.
Yes, in theory the C4 engine has a bigger polycount threshold, and all the fancy shaders and effects imaginable, but if you try to make mid-poly foes with sophiscated shaders applied in a fully shadered high-poly environment, you`ll soon see the limits there, too.
FPSC with 1.17 allows good shaders on surfaces, no matter if segments, statics or dynamics (check out bonds examples), and with 1024er textures of high quality, you can get a very sophiscated look out of it.
However, the polycount is indeed a problem for FPSC. Yes, you can go past the 100k mark, but with performances ridiculous compared to the performance you have with an very old Engine (let`s say Unreal 2.5 or Painkiller) and 500+ k polys.
Also, FPSC can`t handle crowds, C4 can to a given point (again, both can`t match with Unreal tech or similar). So if you wanna prototype with FPSC, be sure to focus on FEW but HARD enemies instead of throwing the player against hordes. And you have to stick to the grid. Yes, you COULD do open areas with cool organical environments (rolfy showed that first, meanwhile several others followed), but you`ll run into problems that you won`t get as long as you stick to the Grid system (which doesn`t mean 90 degrees angles only, take a look at the hive pack or ad rounded corner segments to avoid that).
All that said, would prefer C4, especially when you think that C4 also has Mac, PS and Xbox support.
However, the biggest advantage of FPSC, ESPECIALLY when it comes to fast prototyping is the workflow and the speed with which you can punch out playable results. We work here with Unreal 3 technology, we worked with Cry 3 tech, we spent a year in the Painkiller engine. And still, when I want to test a basic indoor level idea I have in mind, I fire up FPSC and get something that can visualize my imagination within 2-3 days. No chance on that with any other engine.