I'm delayed in going from B3 to G0. I window-shop for E6850s and Q6600-G0's, waiting for Penryn, when I'll probably then wait some more.
Just based on info absorbed here, in the news and reviews -- they went from 65nm to 45nm, packing more into less space. I'm guessing the most vulnerable parts of the CPU for damage from heat haven't changed much.
Get the spec for the TCASE temperature threshold from Intel. That's your guideline. Unless you can find some new information in web-searches for the expected difference between TCASE and TJunction core temperature averages, I'd also stick to the older guideline that it's supposed to be 10 to 15C. But of course, you could simply check the difference by running temp monitoring software that reports TCASE while running CoreTemp at the same time.