I've been using MEP v5 on top of GWX and it looksi nice. Didn't know v6 exist though.
For higher resolution I use Ahnenerbe WideGui 1920 x 1080.
http://www.subsim.com/radioroom/showthread.php?t=215433
4 GB patch is highly recommended in case you haven't got it already to prevent any memory problems running these upgraded textures.