and the other fact that I think the G3 chip itself has a heatspreader on it (not quite sure on that) which the pad/stuff rests on, it may be disapiting a fair bit of heat through that.

Click to expand...

The daughtercards that Apple used in the WS/PDQ/Lombard did have a spreader clipped onto the CPU, I have not tested how long that would keep it cool but damn, that is really not much surface area. My lombard daughtercard is as good as toast (it no longer has one of it's L2 chips) so I could test with that tomorrow.
I may be wrong but 30 mins seems like a long time to run even a G3 on only it's spreader in an enclosed notebook chassis with no airflow at all... just my opinion though. This can be tested tomorrow with my lombard.