Lets talk about the hands in the range you just mentioned above. (x9)9 would play this way if he caught a second pair along the way - so that includes (95) & (9T), same with (TT), do you think (JJ)9 is also possible?
Yes, its less likely within the range based on card removal, but it is possible... therefore we need to include these possibilities. We should also note that since he is a pretty good high stakes mix player (on average over a mix of games) he is less likely to not overvalue a straight vs Hero's river c/r range - but it is possible of course.
I gave the villain a range where he will have at least two pair by 5th along with straights, trips, and flushes on 6th. I also factored on 7th, villain flashing one of his 4 boat cards (which depending on what he had underneath could rarely give him quads). I discounted totally rolled up 9's from his range, as according to your friends read, he would slowplay that until 6th against especially against the hero's dry board.
ProPokerTools Stud Hi Simulation
600,000 trials (Randomized)
22d|3c6d6h7c|2 88.53% (531,160 wins, 0 ties)
*h*h,55,95,9T,9*,KQ,87,jj,TT|9hTs5hJh|J, T, 5,9 11.47% (68,840 wins, 0 ties)
I concur with how the hand was played except for 3rd where just calling is best. If it wasn't for the huge ante, I would fold. I included (TT) in the villain's range that he would generally slowplay until 6th to give him the strongest range on the river. Also included (55) that would make for an optimistic c/r on 4th and got lucky on 5th.
I don't feel that the villain necessarily has to have a boat in order to 3bet our c/r on 7th. I would put a 4th bet in as even if the villain has a boat he won't always 5bet it, as he would have to fear a higher boat or quad 6's putting in a 6th bet. Straights and flushes and even trips are such strong hands HU that frequently multiple bets go in on 7th. I think the liklihood of our hand being best is too great to pass up a chance to put another bet in. It's very infrequent that both opponents boat up on the river, especially HU, although it can't be discounted. I think the 88.5% is pretty close to the certainty that we have the best hand as I would expect the villain to be confident most of the time that straights and flushes (infrequently trips) will be ahead of our c/r range (unless for some reason he believes that we will only c/r boats on the river). Our hand could look like a 7 high straight, rarely trip 6's, and even on rare occasions going for thin value with A's up (although his board does look a little scary). He could also be 3 bet bluffing a non-zero percentage of the time using his board and how strong a 3 bet against a c/r on the river looks. All these assumptions are opponent specific as against some, I would expect my opponent to have a bigger boat the majority of the time. I would expect a decent mixed game player but not necessarily a strong stud player to overvalue straights quite often HU. It seems that according to your friend's read, that 4 betting his strongest hands (the hold'em range) would tend to indicate absent any other reads that he probably is mostly a hold'em player and therefore play his hand according to the value that he perceives it would have in hold'em.