all character / classes were tested in crescent reach.
standard is 10 lvl 1 mobs to get to lvl 2. example = human warrior.
int casters (try a human wizard) also take 10 mobs but if you look at the bar on the 9th kill and compare to the warrior, its obvious they get a small bonus, it looks like about 10%.
anyway, would have to box some higher level toons to see if bonus still applies at lvl 60+, may do that later, have a lvl 62 troll SK and a lvl 60 woodie druid. Once I get the druid to 62, can compare directly, the troll SK should have a huge bonus if it is the same as going from 1 to 2.
I suspect theres some hidden modifiers that only apply at lvls 1 to 50. I know Rash posted about the exp mod for lvls 50 to 60, it was put in to smooth them out.