Well, on the first question, short answer yes, long answer no. I think it does actually render faster, but you'll probably never use the quicker render speeds as you can now crank the renderer up to high heaven. as far as I've heard bryce works better on mac than pc, since apparently it was designed for mac... It's very stable, infact I don't think I've ever had it crash without a good and easy explanation, and tho alot will disagree, yes I think its worth upgrading, hope that helps