The game runs fine on my system with win7 64 bit, even over areas with lots of buildings I get no stutters from texture loading.
Resolution 1600x900, fps anywhere between 30 - 70, depending on the area you are flying over, saw fps spike to over 90 in external view over the channel with about 8 planes on screen, more in combat at the time.
Settings are model detail high, textures original, visual effects high, everything else to medium, ssao on, clouds, shadows, roads on.
And Heliocon, could it be that you are mixing up amd gpu and cpu?
Ben, I am on a very tight budget as well, took me a very long time to buy everything little by little, my advice go with what you have, you can always expand later. I do agree though if new cards, motherboards and cpus (waiting for the bulldozer) will come out later this year prices for state of the art hardware now will fall then, and you even have an AM3+ MB already then.
However looking at especially video cards, one could almost buy a new one every half year, so settle for what you have, expand later, don't get hiped into the hardware ratrace. Only the smalest percentage of gamers can keep up with that financially, I most certainly cannot. No clue how others do it but I got bills to pay and a family to feed, oh and darn it, the family even wants a roof over their heads

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