I'm always amused when people talk about mercs costing you XP. It's really situational, and not that cut and dried, IMO.
One of the big factors is the synergy between your class and the class of your merc. But here's where the real determining factor comes from: If you solo, you get 100% of the XP, obviously. If you molo (fight with the merc), that counts as a second group member, so that's worth a 20% XP bonus. So we divide 120%/2 = 60% XP per char (with the merc throwing out his 60%, since he doesn't "level"). So with a merc, you get 60% XP vs. 100%, or 3/5ths. So if you kill mobs with a merc at 5/3rds of the pace (66% more mobs in a given time frame), then you're even. If you kill less than 66% more, then you're leveling slower. But, if you killing more than 66% faster, you actually level FASTER with the merc, even though you're sharing XP.
My guess would be, if a Pally can solo, that means he's tanking, obviously, and already healing himself. So adding a DPS merc will require no extra mana or attention from him, and will be purely helping to kill mobs faster. So I would say try it both ways, and see if fighting solo really is faster than molo.
In my case (Druid), moloing really was slower than soloing, because druids can't tank, and can't heal worth crap til higher levels. And with mass reverse charm kiting available, that was truly faster. Now, at higher levels, I box 3 chars (DRU, ENC, MAG). I've tried it both ways (with and w/o mercs), and with mercs is way faster.
(As a side note, here's the calc: 3 person group gets 40% bonus, so 140%/3 = 46.6% XP/mob, vs solo. With 3 mercs, it's a 6 person group. Without getting too long winded on how they figure XP for 6 person groups, it's 180%/5 = 36% XP per mob vs solo. So it's 46.6% vs 36%, which means the 6 person group must kill 30% more mobs in a given time frame vs a 3 person group. This is no problem at all.)
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Tatanka Wolfdancer, 87 Wood Elf Druid
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