yea i always forget about flight sims with thier huge draw distances... mostly because i find them boring as hell
as for GTA IV no need mentioning that POS its a fun game but a bad console port, badly coded for pc, for the graphics quality you get for a really powerful mturm windowsachine its just badly done , my 450's in sli aren't the strongest out there but my machine stutters sometimes, but in my defense one intel systelm i helped a friend build with an i7 950 and 2x 470's in sli also gets stuttering and occational freezes on gta IV
as for the computer its just an odd time, sandy bridge is awsome... tbut there's the cougar point issue to deal with knowing you might need to use a pci slot to get proper sata connections or in a few years see them degrade isn't the best proposition, and AMD has been just revising the same archetecture for a few years now (though to be fair i love my phenom II 955 i can't wait for a decent upgrade to appear it'll be SB (or possible ivy bridge) vs bulldozer once the benchmarks are out for my $
also to confirm above bulldozer processors will NOT be able to go into a am3 mobo it will be am3+ but you can put a am3 processor in a am3+ board
as the OP needs to buy now i'd say it really depends on your budget, i'm go with whatever SB is out personally and just wiat till the fix the p67 issue and then rma the board for a proper one sne you said you can't wait for BD