I'm working with an older AMD machine and its been incredibly reliable for me.
Unfortunately, I can't comment properly for the new processors but I will say this, AMD is very modest when detailing the specs for their products.
Here is a good site to check out:
http://www.adkproaudio.com/benchmarks.cfm
Scroll down to the Cubase 4 test.
Personally, I would wait until the new AMDs get all the kinks worked out.