I have found that without either hand holding a five-card (or lonter) suit, it generally takes a combined holding of 34 HCP to bid a slam that is over 50%. The popular requirement of 33 HCP comes from antiquity, because it simply ensures that the partnership is not off two aces. With 33, the slam will almost always require a finesse, and frequently a little extra, too, so you will be in a 45% slam at best. Therefore, I would never consider 6NT on this hand. With four small hearts, I would definitely use (Puppet) Stayman, but finding a 4-4 heart fit doesn't necessarily make slam a good bet, either. First of all, partner's hearts almost certainly need to be AKJx or better, and even then the slam will almost certainly be on the heart finesse AND a 3-2 break, because there will probably be one loser in the side suits. So I would be quite conservative in a heart contract. Maybe the way to go is to look for a 4-4 MINOR suit fit and ignore hearts, by starting with 3S. That seems to me to offer the best chance, as some losing hearts may well be discarded.