Depends on the break format too.
20 may be excessive. I kind of like the idea that if a world class player
plays at least "average" then the other guy still gets 3 chances at the table.
Sort of like baseball's 3-strikes-you're-out.
You'd think the top pros would run out everything in 8-ball on a standard diamond
and routinely put up 10 packs. But usually a little bad luck prevents that...
dry break, tough layout, funny roll, whatever.
You can look at some of the TAR 8-ball matches from the past,
and in some cases the number of racks run in a row isn't that huge.
Corey vs. John Schmidt: Highest package is a 2-pack.
Darren vs. Orcullo - highest is a 3 pack
SVB vs. corey - shane had a 5-pack
Busty vs. Alex - 7 pack, OUCH!
I think 7's and 5's are not gonna happen unless the table is breaking friendly
and you have monster breakers like shane and busty.
The other players, even top-tier guys like dennis, are maybe gonna top out at a 3-pack.
Which means if you have a race to 10 or 11, everyone should get 3 chances.