Ah, finally a member... Been reading since Civ 3 and never joined...
Anyway, I have to chime in on the performance, it is a dog! I actually just built a new system, inspired in a lot of ways by Civ V being released. It is Core i7 980X with turbo up to 3.8 GHz, 8 GB ram, an SSD, and a pair of 460 GTXs in SLI. And, it takes 2 or more seconds per turn from the first turn (large map, default settings)! As the game progresses it gets worse, like 5 or 6 seconds or more, and it is especially bad if a war is on and lots of units are moving. Oddly enough CPU utilization (even individual cores) never seems to get above 10%.
Anyway, it is frustrating, because it seems like the game pace is slowed anyway, and the turn times kind of make it a crawl.
Also, I had to turn my graphics down to medium, cause it was burning up the cards (90% utilization on one, 40% on the other, and lots of heat and fan noise) on high, which is odd cause it doesn't seem like it is that intense a graphics game.
Seems the game is very inefficient right now, hopefully a patch will a dress this, as I have been having a lot of fun playing...