Just wanted to add that I am making my way through this game currently, on the following rig:
C2Q 6600 OC'd 3.24 GHz
4 GB (2 x 2) OCZ ReaperX HPC PC8000 DDR2
2 x Seagate Barracuda 7200.11 500 GB w/ 32MB Cache
2 x eVGA GTX260 SLI OC'd to 636 / 1371 / 1107
2 x Acer X213w 21.6" widescreen monitors 2500:1 contrast ratio @ 1680 x 1050 res max
The game ran great when I first started playing, but CPU bottlenecking was obvious - if I left Thunderbird running, for example, and Growl popped up a notification, poof, instant (but temporary) slowdown.
Upon installing the 186.18 along with the eVGA SLI patch (which seems no different than the nVidia SLI patch) the game started running a bit more smoothly, but the best feature I like is that the drivers allow for multiple monitors even with SLI enabled.
The game may not be the best storyline of the year, or the best graphics of the year, or best technical design, etc...but the sum total is still one of the top titles thus far of this year.
I have a Core i7 965 EE waiting or a home (mobo and RAM) and then I can fully explore the differences (to a point - the RAM will be faster, and more than likely, as someone noted in earlier comments, I'll have the same issue as here - notably that there is more RAM on the i7 system than there is on the current C2Q system....
But as it is I experience no lag whatsoever, and this is making the game play extremely fun. It is also a game that I am going to replay a few times, and that is the true test of whether I like a game or not - re-play-ability. This is going in my cache of recent games like Mass Effect (going through it for the 4th time) and Toca's Race Driver G.R.I.D. (going through it with my 7th profile). A definite keeper.