Should I bid that grand slam?

I got an email the other day from a good friend spending the winter in Mazatlan, Mexico. He held:

♠	K863
♥	AKJ32
♦	J86
♣	A

His partner opened 1S. He gave a game-forcing spade raise (much better than a 4C splinter, in my opinion) and found out about short diamonds opposite. He hopped into RKC and found his partner with two keycards and the queen of spades. He was wondering if he should bid 5NT (asking for kings), 6S, or 7S.

Here's the auction up to this point:

1S - 2NT
3D - 4NT
5S - ?

There's a little-known extension of Roman Keycard that I'd like to share with you. Let's say that the trump suit has been irreversibly set, as in this auction. After the number of keycards have been shown, you can ask for kings with 5NT (We strongly recommend that the response to 5NT show specific kings rather than number of kings) as a grand try, but there are other grand-slam tries available. We play that bidding a new suit asks for third-round control of that suit.

Without third-round control, responder bids 6 of the agreed trump suit. With a shortness control (a doubleton) responder bids seven of the agreed-upon suit. With a high-card control (the queen), responder does something else interesting. So let's give opener a few sample hands on this auction:


1S - 2NT
3D - 4NT
5S - 6H!
?

Hand A:

♠	AQJ72
♥	764
♦	A
♣	KJ63

Without third-round control in hearts, responder signs off in 6S.

Hand B:

♠	AQJ72
♥	76
♦	A
♣	KJ632

Responder has a doubleton heart, so bids the cold 7S.

Hand C:

♠	AQJ72
♥	Q64
♦	A
♣	T863

Responder has the queen of hearts, so his job is to do "something interesting". His partner already knows about the aces and the queen of spades, so responder cuebids 7H to let his partner choose the right grand slam.

Hand D:

♠	AQJ72
♥	Q64
♦	A
♣	K763

Now responder has something "interesting" other than the queen of hearts. He cuebids 7C to show both the queen of hearts and the king of clubs. Now the asker can count top tricks-- 5 in spades, 5 in hearts, 1 in diamonds, and the A and K of clubs-- 13 running tricks without ruffing! Over 7C the proper bid is 7NT. It's not only the top-scoring grand slam, but it's the safest one!