Considering that the computers at my school where I want this to be able to play can barely run OpenGL and require all textures to be a power of 2 in size, I thought I'd put it down to 512x512 just incase. It would be using practically the same amount of memory either way, but this way I can be definite that it will run on older machines.
(We're talking horrible beige clacky keyboards and towers here in some cases, not a pretty sight)

Thanks for the info though, was not aware of 4096^2 textures being supported at all