Spanish 21 Sim
That is great RJT!
Below are the rules. The 777 bonus is neglible since it happens so infrequently.
A player 21 always wins.
Player blackjack beats dealer blackjack.
Player may double on any number of cards.
Player may hit and double down after splitting aces.
Player may surrender after doubling, known as "double down rescue." The player forfeits an amount equal to his original bet.
A five-card 21 pays 3 to 2, a six-card 21 pays 2 to 1, a seven or more card 21 pays 3 to 1. However, the bonuses are not paid if the player doubled.
A 6-7-8 or 7-7-7 of mixed suits pays 3 to 2, of the same suit pays 2 to 1, and of spades pays 3 to 1. These bonuses do not pay after doubling.
Suited 7-7-7 when the dealer has a seven face up pays $1000 for bets of $5-$24 and $5000 for bets of $25 or over. In addition, all other players receive a $50 "envy bonus." This bonus does not pay after doubling or splitting.
Dealer stands on a soft 17.
8 Spanish decks are used.
Late surrender on the initial two cards.
A player may make an insurance bet of half of their initial wager even after receiving a blackjack paying 3:2
Best sim I can think of is Hi OptI with a TC of -4 as you suggested. 75% Pen and flat betting.
I think the double down plays vs dealer pat hands could be worked out using simple probabilities. For example a 10 vs a dealer 17 has six ways to win double the initial bet, one way to push, and 5 ways to lose the initial bet. I think this makes it a better play to double than hit.
BW