Which GTX 460 should I get ?

I am wondering which GTX 460 video card I should get for my computer I was going to go for the 768MB initially but then read a review that suggested the 1GB version should have a better lifetime so I went with a 1gb version for 257$ CAD. But I am really starting to think I should take a 768MB superclocked with lifetime warranty for 235$ instead of even a 1GB superclocked with lifetime warranty for 279.99. I am hoping to eventually run SLI of the one I will choose. I already went over budget for my computer so at this point I just want to make sure I get the most bang for my buck. Thanks