OK rein interessehalber hab ich mal gefragt und von Pete bei Hughes folgende Antwort bekommen:

"You can turn a TH400 10,000 RPM without a problem, but it requires billet aluminum forward and direct drums as well as a valve body with a clean neutral shift pattern (P-R/N-1-2-3-N). You can do the same with a TH350, but it still requires similar upgrades. "