Aces High II performance is not tied to any specific hardware. We do not favor anyone.
Our in-house dev systems are pretty low end, actually. HT has a 2.4Ghz P4 and an ATI 9600XT, and Sudz has a 1.8Ghz P4, and a GeForce Ti4600 card. I use an 800Mhz P3 with an ATI8500.
SLI has to be done by NVidia. There is nothing we can do to add support for that.
Dual core AMD CPU's have a problem in XP as Aces High II is one of the few true multi-thread games on the market. And XP has a bug with multi-threading in DirectX, when using dual core AMD CPU's. Microsoft does not appear to be in too big a hurry to fix it.
Stay off the bleeding edge and you are less likely to get cut. Best advice I can give.