Is it more power, though? You'll be able to kill people faster, but you'll lose far more games than you'll win taking up 10/10 or 10/15 slots in a BG, never mind rated BG's. The 15+ slot BG's aren't in the rated queues (for good reason - you can hardly call AV PvP).

10boxing PvE content seems like it'd be a fun challenge, but there's just no real PvP format in WoW benefits 10 more than 5.