also what benchmarking tools do you use and what is the score of the 470 in them?
No, I don't have a 470, look at my signature. I just compared my benchmarks to other peoples benchmarks, and thats about what happens. THe GTX260 will outperform a single 470 sometimes, but not all the time, and if it does its only a handful of FPS. Granted I do NOT have the 216 version, but that doesn't make too much of a difference.
The biggest problem with your setup is that even if you did get more performance (versus the GTX 470), the cost for that performance would not be worth it. You're looking at a motherboard upgrade, and I honestly don't see you finding GTX260s that cheap either.
You'd also be putting money into old tech, loosing DX11, and having more power consumption/heat. I'm happy with my GTX 260 SLI, but if I had a single GTX 260 now I'd get a GTX 470 as an upgrade.
EDIT - Oh and you would need a PSU upgrade if you went with GTX 260 sli, as well.