650 Mhz -> 702 MHz report and questions

[nitro2k01]

After running my 600E at 650 MHz for a few months, I finally decided to take the last step and overclock those final 8%. It was really an easy and painless mod. (But on the other hand, I'm pretty decent with the soldering iron)
But what bugs me out is that during the first day, I got random 108 errors at startup. They seem to have disappeared now. Really weird. 108 is apparantly "Timer bus test failure", which seems reasonable.
Another thing I wonder about is the maximum acceptable temp. It's not uncommon (Even at 650 MHz) for my CPU to reach 60-80 degrees C. It seems to keep on rolling, but is there some risk for long term damage? Can I help reduce the temp by replacing the plastic mat thing on the heatsink with pure arctic silver? Will it make a difference in my case? Or is a 600X fan the only viable solution?

I'm also curious as to exactly how the mode works. Does the 1k resistor only affect a high-low signal, or is it part of the oscillation circuit, so you can (Theoretically) replace it with eg a 820 Ohm resistor and push the speed a bit further? (Given that the rest of the components can handle the higher speed.)

[nitro2k01]

I've edited the caption (Added the word questions) so I'm giving this a bump.