On further though, I need to know how the opponents are likely to bid my hand. General considerations are trumped by particulars. If the opponents are not likely to bid game, I have to be in 6C. If they bid at the 6-level, I probably should bid 6 something. I don't think I can make 7N or 7C; this depends on Partner holding specific (unbiddable) cards.
I think 7N depends on Partner holding the guarded 9 of Clubs or a guarded 7,8,9,10,or J of Hearts and a guarded K in either Spades or Diamonds (or a guarded Queen thereof and an opponent having a single K). Partner could also hold several Hearts to two honors, like KQx.
After further considerations, I'll still bid 6C. I's a guess. The preempt worked.