If this is all correct, then why do the reviews (in the links provided) show lower frame rates? Or do we not just notice them dipping below 60? I'll check fraps once I get my new card, just wondering for now.
Going below 60 isn't going to make the game seem unbearably slow. Going below 30 does.
Why is SP more taxing than MP? MP has more stuff to render per screen I think, at least at compared to most SP missions.
Some members have reported that some of the campaign scenarios (especially at the end) have lots of dynamic things that litter the screen like lava, zerglings, etc. I wouldn't know from experience, only from member postings here explaining the inevitable slowdowns near the end.
I suppose the blanket statement "MP is more taxing than SP" or "SP is more taxing than MP" is just bound to be wrong in several instances. To be sure, there probably will be instances in MP where it will be lighter than the heavy SP scenarios, and vice versa.
Regarding maxing "a game that isn't out yet", we know D3 will be DX9 native and use the Havok engine and probably be a little more taxing than SC2, so we can make some good guesses, i.e. whatever can max SC2 will probably get close to maxing D3.
We can all make good guesses, but it's no guarantee, I suppose that's just what the other posters are trying to warn you about. Anybody here can give any advice about it, especially advice you would want to hear in the first place. For example, I honestly think a GTX 460 1GB will be fine. In fact, I think even something like a 5770 1GB will do, and I'd gladly offer this "guesstimation" if anybody asks. There is, however, no guarantee I will be correct, nor do I pretend to know for sure, so when Diablo III comes, and neither card does the job... well, it was just a guess
However, even at the risk of "guessing wrong", I still believe 460 1GB or even a mere 5770 1GB will be more than fine for gaming, since it has been "the Blizzard way" to make the game as accessible as possible to most people. There is a bit of doubt, given that you do have a high resolution. I am not too worried about guessing wrong though, after all, it is just a guess.