re: Poker & Stud/Omaha....Lo
As for the eight part yeah, the forms of high-low we typically play today have an "eight or better" qualifier for the low hand, so you have to have five unpaired cards all eight or lower to have a low hand.
This means in some cases you know either there won't be a low hand this hand or that your opponent doesn't have one. For example:
In Omaha8, if the board is KK4T2 there won't be a low hand because there's only two cards under eight on the board and your all have to use two from your hand - the lowest hand anyone could make would be T4X2X and that doesn't qualify.
In Stud8, if your opponent is showing XXQJ39X then you know they don't have a low hand either, because they have three cards over eight showing. The lowest hand they could make would be 9X3XX and that doesn't qualify either.