tbh, there are no benchmarks for games under a mac because there isnt any, so we dont know if a pc will beat it or not
And graphics card vendors havnt made there stuff compatiable because there isnt a decent games to run on a mac, hence its not profitable for them to do this.
Its just simple business at the end of the day....and if Nvidia did go out of their way to make their graphics cards compatiable with macs, then im sure alot of people/gamers would make the swap.
what im trying to say is, if software/hardware was made available to both x86 systems and macs then whats stopping people using a mac as you would a pc?