Please excuse me if the answer is out there all over, or if I'm posting this in the wrong section...
I've seen a couple of tests as of late, and the ATI cards--as a group--don't perform nearly as well as the nVidia's in FSX. I not a gamer but I want to do Flight Simulator with my Dell 3007WFP. I've already purchased the pieces (to include Q9450, MSI X48C, 4GB PC2 8000, and a HD 4870). According to the testing results I've seen on THG and elsewhere, the 9600GT in the family machine would be a better choice if all I was going to do was FSX. Hard to believe the Radeon drivers are that bad in FSX; it seems there must be a more fundamental reason why but I haven't been able to find anything on this...surely, someone out there has an explanation and maybe a fix…I was planning on adding two side monitors driven by the 4870 at a later date, and the driving the 3007 with a 4870X2, but now I wonder if I should be instead considering nVidia stuff (gasp!).
FSX from what I've seen really beats up on any graphics card, but I guess the main reason it'd hate on Radeons is that it could be Nvidia-biased, as most games of the last few years have been ('The way it's meant to be played.'). If that's not the case then I'd suspect that maybe ATi didn't really take their time working on their drivers specifically for FSX because it's not exactly a mainstream game.
But really the graphics card seems to play second fiddle to the CPU sometimes in that game based on the charts so that maybe the more important factor here. I mean, an HD 4870 has enough raw power to handle just about anything out there and in terms of pure muscle eats the 9600GT for breakfast. Probably if you get that quad core CPU up into the 3.2 - 4.0GHz range then it won't matter much whether your card is Nvidia or ATi anymore, but that's just my guess.
I am aware that FSX is CPU intensive, and I was planning on the overclock (hence the PC2 8000), but the difference isn't minor: it's pretty serious and the ATIs don't seem to "come back" at the higher resolutions (remember, I would be doing 2560 X 1600). Check this last test on THG:
and it's all over the map with the GF8800GTS in SLi pulling up the rear behind the super power cards like the ATi X1300 and the GeForce 7300GS & 8400GS. That's pretty serious, OMG both companies should dedicate all their resources to this one title ASAFP !!
This game is not for graphics cards at low settings you could play at 2560x1600 with AA on the HD2900, GF8800GTS/GTX over a year ago, it's not about to stress the new cards much more at 1920x1200. Main thing you want is to keep the min fps above 20 for a fluid experience, average doesn't mean as much really.