you should probably avoid 512x256 maps, or combine 2 into 1 512x512 map )if they only tile in one direction) otherwise I think blitz will scale the map up to 512x512 anyway internaly, the scaling usually reduces the map quality by bluring, and probably has other overheads too.
so allways try and use power of 2 square textures, and multiple textures on one page where possible.
so allways try and use power of 2 square textures, and multiple textures on one page where possible.