Quick primer on CPU upgrades for CUBE?

[Robert Everts]

I'm sure a lot of this info is available on Cubeowner's FAQ, but I'm wanting some real-world experience. I'm thinking about a CPU upgrade for my cube. The 1.2 Sonnet one is tempting and near my price range. I've read about the different versions of the G4 (7445, or whatever). Are these real concerns? And is there one upgrade that is just the best bang for the buck? TIA Cubists...