@Oliver: What about using vertex texturing for the texture problem?
Instead of having a blendmap use the uv-coords or other data of your terrain to blend the different textures.
This should be faster to load (could be loaded with the normal terrain data) and rendering as well (- 1 texture-fetch)

The resolution would not high enough. My terrain has a resolution of 32x32 vertices. But the blendmap is 128x128 px.

Oliver2s, your methodik sounds quite impressive.
But let us say there are suppose to be villiges at surtain areas of the world, how would you do that?

So what I am looking for is to create alot of islands (6-7, you sail to them over the ozean per boot) which each have 3-5 of the the size of the landscape terrain (3dgs car templer demo).
That should actully be passable with the acknex engine.

You mean to avoid a nexus overflow?

Yes.
While you are on one quite big terrain, the otheres which are far away (you have to travel per ship) just are (with everything on those terrains) passable and invisible until you reached a surtain distance.
In that way you could make a really big world with alot of "countries" and towns to discover.

The questin is, how big can a terrain be without killing fps and nexus?
5 times as big as that terrain from the car demo would be great!

You just put more information in the level format and stream that from disk? I don't quite see the problem, loading terrain chunks on the fly isn't much different than loading models on the fly and placing them in the world.

its not about scale, but about how much details and objects you have

Exactly. Hence why you want the streaming in the first place.
I assumed that was the premise of this thread?!

maybe this can help (libAsset by JustSid) (I have not tried it but will soon): http://www.opserver.de/ubb7/ubbthreads.php?ubb=showflat&Number=427781&page=1