PhilKing, on 2015-December-22, 19:09, said:
Bidding a borderline grand slam is bonkers if it is unlikely that slam will be reached elsewhere.
Indeed, if we assume that the other table land in 4H (assuming nv) and slam is one off undoubled if not making:
6D: +10 if it makes, -11 if it goes off. (52.4% chance for break even*)
6H: +11 if it makes, -11 if it goes off. (50% chance for break even*)
7D/H: +14 if it makes, -11 if it goes off. (44% chance for break even*)
* if your only options were playing 4H, or that particular slam.
However, it is very wrong to think that the 44% chance for break even for 7H/S is right. If we are always bidding at least 6 (and the other table is playing 4H), then are gaining an extra 3 imps (assuming we were always playing in 6H if any small slam) if it makes 13 tricks, but losing 22 if there are only 12 tricks, that makes our break even point when deciding between 6 and 7 at 92% i.e You must be pretty damn near certain it is making.