My brother and I bought a similar device last year or so and ran his 500 Athlon at 650 without additional cooling.
Pretty darn scary to break the cover off a CPU with a screwdriver, your heart is pounding and you are pretty stressed by the end, but it turned out really good and isn't too bad if you are careful.
Hope this helps.
Ouch!! I caught my floppy in my PKZipper.