Oce the color depth of the texture is decreased to 256 it gets a bit pixelated and loses many details even if is big as 4096.
I made one whit som high quality photos but the resoults wheren't that great and ofcourse it was a 4096 waste of time that hurted alot. The EMB series didn't really helped.
So, my question is : What is the best size for a high quality texture for Deus Ex or is there some kind of technique to avoid losing the details

Did you make sure to use the D3D9 or D3D10 renderers?

Of course. and the bump map looked horrible, it was better whithout it.

Well you should probably stick to 1024². That should be good enough, really.

Thanks for the help. I wasn't sure about the size of the new vision textures.
This is my texture:

Whit EMBhttp://img713.imageshack.us/i/shot0004cx.png/
Normalhttp://img710.imageshack.us/i/shot0003g.png/

Some extrashttp://img191.imageshack.us/i/shot0002np.png/
http://img833.imageshack.us/i/shot0001r.png/
http://img29.imageshack.us/i/shot0000i.png/

And as you can see, they are not that great.

New Vision textures are a maximum of 2048² because I work to a x8 standard (so 128², the most common size, goes to 1024²). I think only one texture is bigger than that (the helipad) because the mappers stretched out the 256² texture to ridiculous sizes in various maps.

That said, New Vision textures aren't limited to 256 colour space because it's all done with S3TC/DXT1 compression. I can give you the compile code if you want, seeing as I'm going to release it with the SDK (and I'm not the one who figured it out). But 256 colours, I've found, are generally fine for textures unless there's very gradual gradients in them - the limited colours don't tend to notice when everything's in the dark anyway.

That would be cool.