Just for the record, I'm not against weight saving at all, I'm all for it! I just don't think door cards are really the most obvious place to be looking.
If you are removing the door cards, then i'd strongly urge you to cover up the aperture at least, sharp edges are not good news!
I got my A3 down to 1060kg at one point, and at that time it still retained full glass, door cards, dash, and electric windows!
As far as traction goes - that's largely down to setup and tyre choice, in the wet you will always struggle. In the dry 300ish bhp shouldn't be a problem at all.