I would find a 2000+ by a single 5 boxer to be quite, quite difficult. Impossible? No. But it would be quite hard to accomplish without the right gear, an arena team specifically designed for arenas (probably Shammys) and plenty of practice on how to deal with EVERY combination.

My arena experience remains limited but once you start to get to actual geared and premade teams... the difficulty goes up and the PQ (pally quotient) rapidly approaches 2. Which means they can out heal your AoE blasts (if you are 4 mages 1 priest) and then it is game over. It doesn't take mana to hack you to bits.