this is just a question to throw out there because I was just curious but does the collision fuction in face mode if select does it slow down the game?
this is actually one of the things that slows down games quite a bit. ive been able to get some of my games running quite a bit faster by taking collision off of faces that just dont need it. here are some things you should look for when removing collision:
characters with armatures: collision doesnt calculate with armatures correctly and also lots of characters use many polys. instead use a bounding box
overlay layers and HUD: usually nothing in an overlay layer needs collision turned on
particles and other effects: if you use lots of particles in a game, it will hurt your framerate lots if you have collision on the faces