If I could find some grey-tread tyres here (I'd actually prefer blackwalls with grey tread, by Hutchinson), I'd snap 'em up!
Going to California quite soon, will keep my eyes peeled there.
If I go gumwall, I'm pretty set on the Ritchey Z-Maxs from MOMBAT due to their ease of availability, but for all-black tyres I'd go totally modern and want a very fast and light XC tyre like Conti RaceKing RaceSports or Maxxis Ikon 3Cs.
Chronic indecision is a good excuse to buy both, I suppose.