I've seen many accelerated Cube's for sale over the past few years. 1.6GHz to 1.8GHz seems to be the fastest speeds and often advertised.

If the MorphOS Dev. Team finishes other more important work first, they might want to eventually support such models if it is not too difficult to do so, as they should run MorphOS quite nicely. But, I am sure there are features that are higher on their priority list of things to do (like finishing support for the G4 PowerBook).