I've been thinking about this as I've been going over my copy of Kopps guide again and considering the implications of 5-boxing.

If I am 5-boxing and not doing collection quests then I am going through the kill quests 5x faster than expected so my xp will be less (eg if I have to do a kill 10 mob quest but all characters get credit for each kill then rather than killing 50 mobs I only kill 10 and each char only gets 1/5th the xp the guide expects) so perhaps the tedium of the collection quests makes up the lost xp since I then have to kill 5x as many mobs as I'd have to to get the drops....but even then, if I am only getting 1/5 the xp per kill I'd still only get the equivalent of a full kill per mob by the end so I'd still be down xp from where I expect to be and I dont think the group bonus will help :/

Ah well, think doing the collection quests will still help to keep levels going at the rate they are meant to be so will do them as often as I need to I guess but the maths may need to be worked out still.