Follow-up to Forcing 1NT: An interesting example

In Friday's club game, I picked up this hand:

K84
T7
A52
AT632

Partner, John K, dealt and opened 1 Heart. We play 2/1 game forcing, so I bid a forcing 1NT. John rebid 2 Clubs. Now I could have shown a strong club raise with an artificial call of 2 Spades, since this could not be natural (since I would have bid 1 Spade initially), but (a) we hadn't discussed this treatment, and (b) I had stoppers in the unbid suits, so I bid 2NT, which showed a hand of about this strength and invited John to bid 3NT with something extra. John instead rebid 3 Clubs. What now?

John showed 5-5 or longer in his suits and a fairly weak opener. So he had at most 3 losers in Spades and Diamonds. With my King and Ace, I thought I could cover 2 of the 3 losers. He surely had most of his points in his 2 suits. If he had as little as Axxxx or KQxxx of hearts and Kxxxx of clubs, there is a good play for 5 clubs, since there would be only 1 heart loser and no club losers if the suit split 2-1 which is very likely. Even if clubs split 3-0, he might have the Jack also so we would pick up half of those hands as well. So I thought that 5 Clubs would be a favorite to make, and partner might not be able to raise 4 Clubs when game was on.

Since this is matchpoints, I had to also consider our prospects in 3NT. We should get 5 club tricks, my ace of diamonds, a spade if that suit is led, and whatever else we can score depending on where partner's cards are. I decided that it was likely that we had only one combined stopper in either spades or diamonds, so we would have to take 9 tricks on the run. I didn't like our chances of that happening.

So I chose to bid 5 Clubs. This hit the jackpot, as partner's hand was:

Q43
A8542
void
KJ975.

The clubs split 2-1 as expected, so we lost only a heart and a spade. 3NT would have had no play with a likely diamond lead, and with this 10-point minimum, John may well have passed a 4 Club invitation.

When we checked the traveler at the end of play, 3 pairs reached 5 Clubs, one went down in 3NT, one made a club partial and the other 3 passed out the hand! I think that the pairs who passed it out undervalued both hands. Dealer's hand should be opened since it has a good 5-card major and meets the rule of 20 (total points + length in the 2 longest suits = 20 or more). My hand, which shouldn't be opened in first seat, is a good third seat opener (it is usually good tactics to open light in third seat to preempt the opponents).