I can't believe we are still talking about this. What language are 99.99999% of commercial games written in? Well there's your answer.
If you really think using Scheme will cut down on your development time while allowing you to make a high quality game, don't you think fucking SOMEONE out there who writes games for a living would have thought of that? Don't you think SOMEONE would have written a game in Scheme already and made a million bucks? Thinking you're smarter than the hundreds of thousands of people out there who do this for a living instead of taking their advice is a guaranteed route to failure.
I can't believe you think Scheme is fast because it compiles to C code. All its doing is baking the runtime into the code. You can't even make a fucking struct in Scheme; either you only use vectors (which makes unreadable code), or you simulate it with a named list, meaning every fucking variable access is a tree search or hashtable lookup.
I can't believe you give these functional languages greater than 0/10 on your speed list. We are talking orders of magnitude here. If a game runs at 2 FPS in Lisp, it will run at >200 FPS in C++. This is not an exaggeration. This is the real deal. You need to take a serious look at some language benchmarks.
The only serious 3D game I know of of that was written with a Lisp dialect is Crash Bandicoot, and guess what? They had to write the entire game engine in C++ anyway to be able to actually draw 3D graphics in realtime, and they constantly ran into memory problems throughout the project (because garbage collection and functional languages in particular hog *insane* amounts of memory). The only reason they did is because the lead developer was eccentric; he made an uninformed language decision to his own personal desires for which the company suffered, and that's why it was phased out in the sequels and dropped when the company was acquired.
All this being said, I still say you should write the game in Python. You have not given one single valid reason why you wouldn't use it. You will get extremely rapid development cycle this way, and because it integrates so nicely with C, you can just replace bits of code with native C as things get slow. You will get many more people willing to participate this way because the project will be a) playable in months rather than years, and b) actually fun to code. And guess what else: Python is almost as fast as Scheme! (but still a thousand times slower than C++).
http://shootout.alioth.debian.org/u32q/benchmark.php?test=all&lang=all&d=data&gpp=on&sbcl=on&mzscheme=on&python=on&calc=calculate&box=1