That PSU should run the 9800GTX fine. I would look for another problem.
The q6600 doesn't use as much power as many people think it does. I just set it to 2.6ghz 1.25v and at full load prime95 it uses 56.25 Watts according to Asus EPU.
Of course when you put 1.488v through it and set it to 3.8ghz I'd imagine that number goes up by QUITE a bit.