In truth, you can run an 8 pin 960/950 with only a 6 pin. Once you have the 6 pin (either from psu or adaptor) just hook it into one of the 6 pin inputs on the 6-8 pin adaptor. If it doesn't boot, try the other input. That is how my SSC GTX 960 is connected, and it maintains 1430 MHz boost clocks pretty consistently unless the game is too easy.
Really, the 8 pin is there in case you feel like overvolting. And even then, you probabpy don't need more than 150 watts. Most overclocks max out between 1500 and 1600 MHz anyhow, not a big jump over my stock 1430 MHz boost clock. Putting the memory to 8 GHz (or 7.8) might be of more benefit where AA is often used.
Btw, I got my card for ~$160.