The Only Real Problem with the Massive Boxers I see is I had a WG were 3-4 Massive Boxers took up all the Slot on Horde, and there were very few normal players as they couldn't get in because it filled up.
Personally (just a Suggestion/Opinion), would be fair that someone can go past 25 if they pay up, or in other words, get past a Donation Rank of Supporter on each Acct. In other words, they Contributed so much to the Server, I don't get mad when they kill me compared to the ones that never payed a dime.
I'm staying at 5 because that's when you can do Heroics, BGs, and focus on Quality (or Skill) instead of Quanity (Numbers).