Trouble overclocking ASUS 5950 Ultra, any help is much appreciated

I recently purchased the ASUS 5950 Ultra and i tried using pretty much every overclocking program out there and none work. The one I always used in the past with my other VGA's is CoolBits cause its simple and effective. Now, when i use it with the 5950, i increase the speed by like 5 Mhz intervals and it seems to go on forever without saying that it needs to be dropped down. Whenever i hit the "Test" button, the screen refreshes and the the testing bar goes on to 100% of the bar and then the screen refreshes again, each time with no message being displayed. I got the core up to like 640 Mhz and then it restarted the computer. Could anyone tell me why its doing this. thank you very much.

My system:

Athlon 2700+ OC'ed to 2333 Mhz
ASUS A7V8X-X MoBo
ASUS 5950 Ultra
512 Mb (256x2) Mushkin 2-2-2 Special RAM
120 GB Maxtor HD w/ 8 MB Cache
Plextor 48/24/48A CDRW
Sony 16x DVD-Rom
500 watt aluminum power supply

Why would you possibly want to overclock that beast of a card?

You're probably getting 100FPS+ in every game, do a few more FPS really matter that much? :D

lol yeah it is pretty fast. it just bothers me cause i should be able to overclock it but for some reason i cant. i am trying to see just how far the 5950 can go with overclocking and i want to see the difference in various benchmarks to see if it is even worth overclocking. thanks for the input :D