for something like that I would probably use a displacement map. as it looks loke your trying to get a lot out of the bump map.

I only use bumps for small/medium things, wood grain on a table top, brick textures etc etc.

A bump map alters the normal to make it look displaced where a diaplacement map actually creates geometry to give the detial.

You could try saving your map as a 2048 and give that ago to see if its any different.