ok so heres the deal. I have a 9800gtx+ sli and i want to upgrade to a 260gtx core 216 sli. the 260 sli runs for about $400. and if i sell my 9800gtx+ sli i might get $200 (maybe. doubt it tho.) but if i do thats still $200 out of pocket. So what i guess im getting at it is that is $200 worth upgrading to a 260gtx sli?
The GTX 260 is still a DX10 card. Sure two GTX260s sp 216s in SLI would outperform two 9800GTX+ cards in SLI, but I don't believe that the performance difference is enough to justify the cost. Two 9800GTX+ cards in SLI still offer pretty good performance. If you are going to upgrade then you may as well go with a DX11 card. If you really just don't like ATI for some reason, or have a board that strictly supports SLi, NVIDIAs DX11 cards will be launched in February (or so they say). When that happens you may feel bad about spending $400 on two GTX 260s cards that only provided a modest increase over your 9800GTX+ cards and lack DX11, or it may be long enough for you that you would be fine upgrading again as soon as you needed DX11 for whatever game that truly made use of it. It's up to you.
Or you can buy 2x4890s for $400 - 4890s are equal to GTX275s.
Or better yet, get yourself an ATI5870, aka 2x4870s on 1 card for $400. This card is the most powerful single GPU on the market today. It rivals the 4870x2 and the GTX295, and supports dx11, runs cooler, uses less power, and costs less.