800Mhz is the bottom line i would say for a tablet. My Blackberry bold runs at 624Mhz(intel xscale) and it is painfully slow. Add the much higher resolution on a tablet and your adding a bunch more work for the processor. Idealy id say try get a Atom or Tegra, not sure on the Cortex A8 as wilderbeast sugegsted as ive no experience with them. I heard the snapdragon family of procesors is quite good, though i think there centered mainly around phones
In conclusion, trust Wilderbeast, he has a site based around android tablets i think... atleast someone here does

I can count to banana...