[fromageGB]

Making 5♠ the king ask presupposes that you have an agreed treatment that can make use of the additional space. If you do not, then you can achieve nothing with 5♠ that you cannot with 5NT, and therefore 5♠ becomes a "what's that?" bid. In this case I would read it as a proposed alternative place to play, leaving the decision to partner. While it does guarantee enough for slam, maybe opener has had prior experience of responder's "trump queen showing" responses.

[Zelandakh]

 fromageGB, on 2012-November-26, 04:06, said:

Making 5♠ the king ask presupposes that you have an agreed treatment that can make use of the additional space. If you do not, then you can achieve nothing with 5♠ that you cannot with 5NT, and therefore 5♠ becomes a "what's that?" bid. In this case I would read it as a proposed alternative place to play, leaving the decision to partner. While it does guarantee enough for slam, maybe opener has had prior experience of responder's "trump queen showing" responses.

5NT = ♥K
6m = mK
6♥ = useful extra without a king

How difficult was that? Or you could use 5NT as the useful extra response and keep the ability to ask in which suit (but losing SSAs after showing ♥K). It does not matter which way you do it, only that you have agreed. There are many RKCB/Kickback auctions where there is extra space so you would expect Expert pairs to have agreements on how to use it advantageously.

[nielsfoged]

 ArtK78, on 2012-November-23, 11:55, said:

Perhaps this is a simplistic way of handling this situation, but if a player bids RKCB and makes any non-signoff call next, to me that is forcing to slam.

This is the statement from Art I didn't understand!

 ArtK78, on 2012-November-24, 09:43, said:

You should not enter into RKCB if you don't want to be in a slam missing a key card AND the trump queen.
I know that others disagree with this. That is fine if that is your agreement. It is not the way I want to play RKCB.

After this explanation, even I understood what Art meant: He plays an "unusual RKCB" where entering with 4NT commits his side to slam despite missing 1 KC + trump Q.

 Zelandakh, on 2012-November-26, 03:07, said:

I think it was pretty clear what Art meant. Bidding RKCB says we have enough for slam unless we are missing 2 of the 6 base cards (trump AKQ, 3 side aces).

Despite apparently finding it clear what Art stated, you (Zel) seems to cite him oppositely: as if Art could stay out of slam, if missing 1 KC + trump Q. He cannot!

So, obviously for Art playing "unusual RKCB", 5♠ is 100% forcing and should be taken as allowing a grand slam try from the unlimited partner. Art may even have different definitions for 5♠ and 5NT (and 6Mi).

However, I expect that most of us play "usual RKCB", where 4NT does not commit us to slam, when we miss 1 KC + trump Q, whereas confirming holding trump Q would be slam committing.
Therefore, I started this discussion to find out if anyone playing "usual RKCB" would have an extraordinary agreement of the opportunity to stay out of slam, even if receiving a positive response to the trump Q relay? I believe Fluffy gave a very good example: if the positive cuebid under 5♠ is actually disappointing (such as holding the singleton ♥A, when partner shows ♥K and trump Q/extra length by 5♥).
Another opportunity I considered was if the 5♠ bid could be to avoid bidding slam, when holding basically all side suit values but just Kxxx to Qxxx or even Kxxx to Qxxxx in trumps?
In all cases, Responder is obviously not obliged to pass 5♠, but may bid 6♠.

/Niels

[ArtK78]

Niels is correct in interpreting what I said. If I embark on RKCB, I will commit my side to slam if we are off only one key card, whether or not we have confirmed possession of the trump Q.

And I do not find this to be highly unusual. In many RKCB auctions, you have a 9 card trump fit, and the slam will be at worst on a finesse. Also, you should have sufficient values so that you are not playing a trump suit of Axxx opposite Jxxx.

But if you need to ask about the trump queen after you have already determined that you are missing a key card, I suggest to you that you are already too high in many cases.

[PhilKing]

5♠ is FORCING.

Had partner held the ♠Q and no king, we were slam forced (pard had to bid 5NT or 6♠), so we can't stop when he shows the heart king as well!

How does partner continue? He bids a minor king if he has one, else 5NT to show good hand in context and 6♠ with a dog. In other words, standard Kantar.

5NT would ask for queens.