It's a weird thing. I think that BS2 requires a bit more horsepower, but even if you dial back some settings the improvements to the visuals in BS2 mean that even dialed back it looks better than BS1 at higher settings.
So..LOL..sorry that doesn't really answer your question..
FWIW - I was flying BS2 with a system I built in 2008 and it is doing fine..
BeachAV8R