Do you expect to have adv rune income anytime soon? Might not be worth waiting for (you will be ready for your next 7 by the time) if it takes a long time.

Also, purify first, refine second, so you can refine on the highest purify bonus. That might influence your decision somewhat. Chances are, your 6 started before purify came out, whereas out of all your 4s, at least one have a much better purify.