SLI 6600 gt's or single 6800 gt ?

im looking to upgrade graphics...

i have been waiting along time to do this and i want my decision to last me a while like my last has.. i am moving from a ti4600 (oc'ed) 4x...

obviously i could go for all new top of the line but budget is always an issue with me..

im really debating if i should move to pci-express SLI 6600 gt's
or just stick to an agp 6800 Gt ..

what will be benefit of running SLI compared to a single 6800..

tried reading a bit about on other web pages but seems to be that some say the 6800 gt overclocked will run just as fast as the sli setup becuase of the pipleine situation..

any feedback is appreciated !!!

oh here is the model of the 6600 gt's

http://www.newegg.com/app/ViewProductDesc.asp?description=14-122-208&depa=1

and the 6800 gt

http://www.newegg.com/app/ViewProductDesc.asp?description=14-122-195&depa=1

always was a leadtek fan so it will be that brand of choice ..

scratch that ..
i would rather go single 6800 gt that dual 6600gt's..

most bench's 6800 gt won, and the ones it lost didnt loose by much at all...