My start of the auction is the same to 2NT: 2
♣-2
♦; 2
♥-2
♠; 2NT showing 24-25 balanced. I think there are already four points of note:
- I play Birthright, like several other posters here.
- I chose to represent the hand as balanced despite being semibalanced, because bidding clubs on a strong auction is awful.
- The great clubs and all those aces and kings make the hand worth an upgrade to 24-25. In fact, it's closer to 26.
- I chose not to open a Dutch Doubleton 1♣, which would also be permissible with this strength and shape - partner will only pass with a weak hand with long clubs, which is unlikely, and I can represent this hand as a game-forcing clubs-spades hand by jump rebidding 2♠. I think treating this hand as balanced is superior, but the Dutch Doubleton auction might be interesting as well.
Over 2NT my auction is a little different. West would rebid 4
♣ in my system, showing a slam interest hand with 6(+) hearts. If West chose to bid 3
♦ instead, East's proper response in my system is 3NT - a 3
♥ bid would show 3(+) cards in the heart suit. However, I think the paths converge soon after. Over West's 4
♣ East can bid 4
♦, positive. I agree with mikeh that this is again a pivotal point, East has to realise that their hand is very strong for a heart slam even in the 24-25 range.
Saving some ink and giving the full auction I would bid:
2
♣-2
♦;
2
♥-2
♠;
2NT-4
♣;
4
♦-4
♥;
4
♠-5
♦;
5
♠-6
♥;
P
On this auction I think 5
♦ need not promise the ace of diamonds - West's hand is so limited that demanding an ace seems like an inefficient use of bidding space. As a result, I'm not confident that East's 5
♠ try, looking for a grand slam, is warranted. As West I'd sign off - we've shown the whole hand already (6 hearts, diamond control, mild slam interest facing 24-25 balanced), but it's a bit murky.
With both hands visible the grand slam is a poor proposition - we need the jack of hearts to drop in three rounds (i.e. hearts 3-2 or a singleton jack) and then we have chances for a 13th trick with clubs splitting 4-3 or a squeeze. On a diamond lead our double squeeze chances vanish and we also have to deal with the blockade in hearts (so win the
♦A, cash two rounds of hearts, then club ace and a club ruff which has a small but present extra losing case of a singleton club with the third heart).
As a little bonus, the Dutch Doubleton auction would start 1
♣-2
♥ showing 4-8 with 6(+)
♥, over which opener can bid 2NT to ask for more information and I would treat the West hand as a maximum with a poor suit, bidding 3
♥ in my methods. After this East needs to find a way to push to slam (I'd start with a 3
♠ control bid), and it seems that we have an easier and cheaper auction this time. In practice I'd expect an opponent to be in the auction over such a cheap opening as 1
♣ though, and also we got a bit lucky with the hand. If you think the West hand is a minimum in the 4-8 range (a 6hcp hand is nominally in the weaker half of the range by frequency) East should still probe for slam, but it gets a bit more complicated.