Bonus bet 21? does anyone know a counting system?

I believe it was bally's that had a game with a sidebet for the first two cards. You could bet for a pair, 21,20,19,18, or 17 each with a different payout. I was wondering if there was a counting system that would maximize the betting correlation better than a high/low. Since 9's and 8's become more important ( 19,18 and 17 had high payouts), i feel that counting them as zero would not be the best count. I would appreciate any suggestions.

btw They used to have a bet for the first two cards being red or black. Payout was 3-1! no house edge and the easiest count in the world. Last time they had it, every person at the table was counting and placing identical bets on red or black...I guess that's why it's gone.