From my perspective the only thing we have ever found that matters is the quantity of gear 11 and gear 12 characters across both guilds as a whole. If that number is close it's usually a close matchup, if there is a big difference it's a blow out.
Because bottom line is gear 10 toons don't do well against gear 11/12 toons. It's too big a gap.
For lower power guilds I would imagine the number of gear 9/10 toons would matter, but if your 100 million GP or more the number of gear 11/12 toons is literally the only thing that matters in matchmaking.
