The funny part is that it's typically the high E and G strings that have the highest tension of a normal string set. The low E, B, F#, whatever strings you add below that have usually significantly less tension than other strings.
Depends I guess. Take a 10-46 gauge set on a 25.5 scale length 6 string. Strings 1 thru 3 have 48.2 lbs of pressure. Strings 4 to 6 have 55.4 lbs.