I suppose I can guarantee you that it will run higher than 60- fps for highest settings for both games. I play D3 and SC2 for myself on iMac 27" late 2012 with highest settings, which gives me about 50-70 fps. Considering the Mac Pro's spec, it should just run fine, although I'm not quite sure whether either of the games are properly figured/programmed for a machine like Mac Pro. (I hope someone else can put this in a better word, cause I just can't)
But here's the downsides. Like I said in "figured/programmed" part, SC2 only utilizes one core, only small amount of threads are moved to the second core. Or so I heard. I didn't pay much attention to it, (it was originally revealed in 2007, and have been in development for quite awhile) since the game itself is quite old. Probably 7 years or so since the announcement in Korea. I believe the same goes for D3.