Zanthor, due to the way group XP works with boosting you actually get more XP in a group of 4 lowbies + L70 than you would in a group of 2 + L70 (or 1 or 3 lowbies + L70 even). And at any rate it's simply triple XP per kill while boosting vs not having recruit-a-friend. I guess you're comparing solo kill XP to duo'd kill XP w/ RAF bonus which is true, though why you'd boost just 1 character I don't know.