The stock cooler is a hunk of junk -- it cannot handle even a moderate overclock and over-volt. That's why it went all the way to 98ºC when the ASUS board auto-overclocked. I bet the CPU was actually throttling itself to keep the temp from going higher.
TjMax (max safe core temp) for Sandy Bridge CPUs is 98ºC. Still, you shouldn't run anywhere near that for any sustained amount of time. It can severely shorten the CPU's service life.
To keep Sandy Bridge happy for a long-term overclock:
1. Keep the peak Prime95 core temps below 75ºC
2. Keep the CPU voltage below 1.4v
For that, you need a good after-market cooler.
Cool, thanks Leaps-from-Shadows,
I'm gonna go with a Cooler Master RR-V6GT-22PK-R1 V6 GT Multi-Socket CPU Cooler, seems really good, I was thinking of water cool, or something like corsair H50 or higher, but i'm just afraid of watercooling and dripping something on my motherboard or what not. so might stick with the V6.
Wow yeah that CPU temp surprised me. I don't have an i anything processor so I didn't realize that was within normal range as well.
You probably shouldn't wait around for that cooler to come out because it will be at least a couple of months and we haven't seen any actual review yet. go with a decent current gen CPU cooler like hyper-212 or V6 as recommended by others above is probably the best option.
If you really want superior cooling you are better of making your own water-cooling system. Most of the inclosed systems only do a degree or two better than good air cooling.