I am waiting to upgrade my 2006 MacPro from 2x2.66 duals (5150) to 2x3.0 quads (x5365.) So far I have received my 1st X5365 and fishing for the second one. Can I replace two 2.66 duals with one 3.0 quad for now? I know that this Xeon configuration is possible in theory but have anybody tried this on MacPro1,1 ? What happens with performance? Also, I know that Intel does not officially guarantee operation when mixing different CPUs but has anybody tried mixing one 5365 and one 5150? I can't believe nobody tried this yet?