GTX 460 overclocked fan speed.

I just got a Gigabyte GTX460 and decided to overclock it to 800 core, 1600 shader, and 2003 on the memory (seems like a safe setting, I don't want to go much higher). I am using MSI Afterburner to overclock. Should I leave the fan speed on auto, or should I manually set the fans at a specific speed, say 70%. I ran Furmark and the temperatures level off at 74 C with a fan speed of 61% according to GPU-Z.