At this point I don't think even SD would have an answer for that one. I do know that Civ V and AoE ran rather slow and generated a lot of heat in my GPU on my previous PC, and GC3 has minimum requirements already listed that implies to me that, like any strategy game, using its maximum potential (such as large maps and maximum graphics detail settings) will probably push any system that only just meets the game's minimum requirements,

Also, I know from experience that we (the user community) won't really know the answer to this question until the last very few builds of the Beta text cycle. SD tends to include a lot of debugging code until then (and rightly so).

I have faith, however, that SD will do all they can to make it work well on a PC that has the minimum requirements they have already specified.

There isn't really any way to know yet. Other then x64 bit and direct X 10/11. I can almost guarantee that it will be somewhere in between the requirements for GC2 and the best gaming PC money can buy....

Still, unless GC3 adds some extremely different game elements, it will probably have some fairly low settings. If you turned GC2 down all the way, it basically ran like a board game with icons, and no graphics whatsoever.