GTX 260 216 55nm vs 65nm?

well, if it is evga, only the 65nm can use the voltage tuner.

Get the faster card. The 55nm havent really shown to be that much better of overclockers, plus they use a cheaper heatsink so temps are the same as 65nm.

They use a little less power and allow a slightly higher overclock not by much, like next to nothing.

I would go for 55nm, less power consumption and chances of getting a higher clocked card. Unless you are going water, the OC on these cards are mostly temperature limited, whatever max clocks you achieve on air at stock volts are going to be your final max overclock. Bumping up voltage using Evga Voltage Tuner isn't going to help at all because you are going to be severely temperature limited at maximum oc.