Just letting everyone know that i just fit EVGA GeForce GTX 760 Dual FTW 4GB w/ EVGA ACX Cooler into my x51, replacing GTX660 OEM. It works well and perhaps better than GTX670 FTW (crashed often and high temperature).
Nah man, it's all good. If there is an 8 pin plug, just plug the 6 pin in it. Should be fine. Also make sure you have the 330W PSU. It's is th big PSU and has a ground.
170W Has to be the TDP for any GFX to work.