As others have said if you want to have a system that will last a bit longer with all the new games coming out than you would wise to invest in the 8800GTS.
I just built my system and had thoughts of doing the whole sli thing with two lesser cards... I instead went with a 320mb 8800GTS and it has handled everything I have thrown at it so far... I feel I made the right choice..
I did however get a board and psu that is sli ready so that if I come across another one of my video cards at a good price I can add that be sitting even better...
i have used both the geforce 8600 gt and the 8800gtx, my current beauty anyway i found the 86 gt inferior for true gaming, games such as sup com, lord of the rings online, and bf2142 if the 86 isnt good enough then the 85 most certainly wont cut it. If you have the cash and space get the 88 gts or gtx just fyi they are HUGE bigger than a mens 11 shoe. if you even plan on upgrading to the 88 or running in sli get a big case and a 500+w psu.
Yeah that's whats great about guild wars, it looks nice but isn't demanding at all, I run it on my 9800pro 1280x1024 w/ bloom high settings and I get nothing lower than 30fps, mostly 50-70