I think 4NT should be a general
slam try because there is no other below game.
Natural would be best if partner
held KQJ KJ109xx 9x Qx. It wasn't
easy to construct that hand vs. mine, though
I wonder: ought not partner bid 5 over 5? If I
have three key cards, I'm supposed to bid slam
myself, if indeed, 4NT is key card, but I wouldn't
trust partner to do that, so why should he? Anyway, in
a non-partnership, I'd just not bid 4NT, not knowing
what partner thinks it means, but try 6. That goes down.
Upon further reflection, in a non-partnership, from
now on, I'm playing 4NT as RKC Blackwood or jumping in
response if I don't know what suit is trump