Well after Powerlogix and Gigadesigns, Sonnet has just announced its first dual processor G4 745x based CPU upgrade.
As for the competition, this card set at 2x 1.3 GHz works in all SDRAM AGP G4s (MMD G4s not supported).
If you have one of the first AGP G4 (Sawtooth), you need to make sure that your machine's Uni-N revision is higher than 3. (See here).
More info: http://www.sonnettech.com/