ok thanks rob ill start my endless testing so

From my experience, using a 512 texture instead of 1024 can drastically reduce loading time.

hmm i always use 1024x1024 and it works fine for me, but 2048x2048 isnt very good i think- it takes too much time to load

As both you and Roberto mentioned, it will increase loading time.

Its been a while since i used 3Drad, but, i'am pretty sure .dds files load alot faster than everything else.

I would suggest trying:
- DXT1 for non-alpha textures
- DXT5 for Alpha Textures

Should improve loading performance for the textures, as, they wont need to be converted on load.

From a design standpoint knowing the do's and don'ts of modeling and texturing can optimize performance.

The biggest mistake developers make is creating models and textures that look awesome, but run-time hog a lot of RAM due to them being very detailed models/textures.

The trick is to make high poly models, then apply your high res texture.  Export the texture, then reduce the polygons in the model and reapply the texture map.  The result is a model that looks almost identical to the hi-poly one due to the illusion created by the texture.  Polygons always use more memory than textures do.

You should also consider what your target audience is.  If you want the game to be more accessable to the masses you should use low-poly models with decent sized textures.  If you want to cater to the people with faster computers, you can make more detailed textures and increase your poly count a little.

It also matters what file format your textures are in and if they have transparency or not.  Making a landscape probably won't have transparency, so you don't need an alpha channel for this, whereas something like tree leaves, for example, will use transparency, so you can billboard the modles and apply really hi res texture for realism.

I'm pretty rehearsed in this area and am willing to help in any way I can to make your game a reality.

-Sorv