There are 10,000 FPS engines out there. But, with an engine like Q2's (Quake2), despite the fact that it's now aging, the DLL coding would make it easy enough to convert the game into whatever.
I have the Q2 engine and I've done some serious work on it to upgrade it to a more powerful engine (actually, it's the engine I use for TSFH). The DLL includes the 'rules' for the engine so it's easy to change the way everything works.
Of course, I'm in the midst of a thousand and one projects at the moment so if someone is willint to take the TSFH source and listen to me blab about the interfaces and program calls for forever and a half, they're more than welcome to try.
Heh... TTYL
:op2: Leeor Dicker