At last I managed to complete the render!

I have switched all lights to raytraced shadows, set shade rate to 0.1 (0.02 was really TOO low!) and left textures to 2048.

You can see the result here: http://www.renderosity.com/mod/gallery/index.php?image_id=1305059&member

Thanks for your suggestions!

giorgio_2004 here, ksabers on XBox Live, PSN  and everywhere else.