I'm surprised I'm the first (I think) to post this, but there is a firmware update for the newer G5 PMs. I've installed it on my 2x2.5 GHz PM with no ill effects. The update doesn't give much detail as to what's changed.
My original rev was 5.1.8f3. Now it's 5.1.8f7.
My original rev was 5.1.8f3. Now it's 5.1.8f7.