Does the remaining 8 person group run Turn 4-5 themselves as well? If so it would probably be a benefit to leave one of the stronger people out of the "strong" group to lead the other group. Otherwise you wind up with a "strong get stronger, weak get weaker" problem and the 1 or 2 that NEVER get to run T4-5 with the good group grow resentful and quit. I've been there with FFXI. 6-man Nyzul group but 10ish regulars in the LS. couple of people always getting left out of NI for various reasons. They just get fed up and leave because the "static" isn't even willing to take them along as a learning experience.