I think running a large bore two stroke at a set rpm for long times leads to detonation and possibly other problems. I could be wrong here, but i think i remember jerry hall telling me this once. That this is part of what led to the demise of the 2 stroke streetbikes.
Something about sustained high rpm running being an issue with detonation.
Maybe J.H. Could chime in about this?
If i was to set up a zilla for high speed riding. I.e.  running 60-80 mph for miles and miles, i would think that gearing the bike to run lower rpms could help.
I dont think spinning a zilla to 9k+ for extended times is a recipe for reliability