BAP,
on the fan control on Precision Tune, do you have it set on AUTO or have you considered clicking auto to turn it off and manually using the slide bar and running your fan at 80 percent?
That is where my gtx460 is at. This keeps the temps about 65 degrees and overnight they drop a little.
I would consider speeding the fan up until your temps drop down into the low sixties. This will help stop NANs and EUE's also.
I do not let me gpu temps get into the seventies at all. More fan speed is required.
Hope this helps.
micro...