I use catalyst control center to check my temps and when doin nothing it is at 49-51, when gaming can go up to 80, but usually 70ish.
Should I use Riva Tuner to manually adjust fan when gaming? Like to 70% or so?
That should be fine. The old single slot cooler on my 4850 would idle at 70C and max at 80-90C (and was supposed to do that). GPUs can take a lot more heat than CPUs or other components. It even hit 110C once with no issue (though I replaced the cooler soon after that).