I grouped my SO/SE with my 6X SpS when she was lv 30.
I was expecting the SO to get little to no xp. I was suprised that she was getting about 1-4k (4k at current lvl) per kill. Usually got a little more than half of what she would be getting were she grouped with someone in the same lvl range. But with how fast my SpS could get I was easily getting 1-5 lvls during a hard grind. SE is now 44 after a week of relaxed grinding (and many many deaths).
Was funny to see mobs that aren't agro to me go straight for the SE.
Thers truly not much point when thers 20 levels difference.
First of if thers 20 lv's difference from highest towards the lowest one in a group that person is not counted in towards the party bonus XP example.
And yeah usualy around less then 20 level's difference is a good thing thoght the player can defetively get beter xp without the higher lv players and play with even lv players in a good group.
I say max 5-10 lv's difference more then that you aint earning on it.
There was a note in there about changing the penalty for level gap.. I don't know if it affects this or not, or how big of an impact it has if it does.
Also, it's far more efficient to powerlevel more toons at once. The levelees will get slightly less per kill, but the leveler will get less, meaning your levelees are getting a bigger slice of the pie