1-2k more players would be perfect imo. I would rather not have the population of the PvP side though, I guess nothing you can really control that well though.
More importantly soon AV will be out and if the H/A ratio stays like this it will suck for PvP. How come PvE has such an abundance of allys. Roll horde if you don't have a specific preference so the server becomes balanced. Either that or expect 2 hour ques on Alliance side for AV/WSG/AB. Do it for the server!