By adding more noise octaves and adjusting the parameters, i succeeded to make the texture look less blurry and generally, have more details than the last one.
In other news, i've discovered a driver bug on ATI cards, from Catalyst 5.5 to 5.9. Some operations in a pixel shader get corrupted, and some random, blocky pixels of flashing colors appear in the texture. It does not happen in Catalyst 5.4 nor on NVidia cards. I've email ATI about the problem, now waiting for an answer.
Things are getting quite exciting: my next step is to make a manager and a cache for the terrain's texture, and to generate multiple terrain textures at the same time. I'll then "simulate" what's happening in geo-mipmapping, but on a flat, single-quad patch only, and apply on each patch on of these textures. Then i can work on transitions and potential "seams" problems. If i succeed i'll make a video demonstrating it in the coming days.
The terrain above is generated at 120 fps on an X850.