Actually I have heard the complete opposite, on an IRC channel Weltall did state that the EZPCUSA (non-RP server) is actually has a lot more lag due to the slower (or not as great) Hardware in the server.
But Zeroping has a far more bugged database, that I have heard of. I wouldn't be too surprised if PS did a wipe on Zeroping and the server could handle over 1000 players.