Yeah sorry I forgot to mention that. If it's worth it to go SLI, I will look at around a 700w PSU. The 450w is just for the current build (money isn't a problem btw, I just don't want to spend if I don't have to)
have a look at the CHARTS section of this web site . They will have benchmarks for the 9800 gt in sli .
Personally I'd probably spend the same money as 2 x 9800 gts on a single better card
4890's are under $200 and so are gtx 275's
And since the nVidia chipset mb's have a such a poor reputation if I was building phenom then its probably safer to stick with an AMD 790 series nb and 750 sb chipset board which means crossfire and not SLI
I agree with Outlander_04. The 9800gts is getting pretty old in terms of computers, and spending money on one now would be a waste. It isn't a bad card, but there's better performing ones for a similar price out there.
My recommendations would be to drop the 9800gt/s and grab a gtx 275 or radeon 4890. Either of those will outperform 2 9800gt's.
Thanks for the replies. To clear it up, I havent bought anything yet (I don't actually own a 9800). I've had a look around, and for what I'm going to be doing, I'm going to get a GTX260, and when they come down in price a little more, get another one for SLI. I've also decided to go with a 700w PSU as well for when I finally do get the extra card.