Make sure you have all the latest GFX drivers installed, DX diagnosis report won't help much to fix any driver level issues I'm afraid. From my experience DKS is taxing on lower end GPUs, specially when played at a high preset. I'm playing it on desktop though. I had a few problems with my previous card which was an entry level ATI HD4550 with 512MB of V-RAM and a re-installation of drivers helped fix those. Do a bit tinkering with your graphics settings and see if that helps, try turning down/off features like distance rendering,HDR etc as Raze mentioned. Also at high resolutions using high quality texture requires lots of V-RAM.
