Mine did 634 on the core fine with the stock cooler. I'd probably try 1450, 1550 or 1566 on the shader clock.
I use to use ATi Tool to reduce my 2D clock to 350. I had two profiles I created, one was the OC and one was reduced for when the card wasn't doing much. I would use nTune to jack my fan up when I gamed.
When I installed the TR HR-03 Plus I just flashed my card to 659|2040 with a 1566 shader clock and called it a day. I moved to the TR HR-03 Plus because I couldn't stand my 61-64C idle temps, and yes that was even stock speed. The TR HR-03 Plus is great if you don't need those extra PCI slots. I still have one open at the bottom with it installed. Now I idle 45-47C and load 56-58, depending on ambient room temp.
If you want to keep all your slots and cool the card well, look into water cooling.
Below is a great thread for anyone new to flashing a GTX. The best approach is to edit the BIOS that shipped with the card and flash it in. Of course, folks should save said BIOS in its pristine state.