Wheel size, track width, and handling

[dekaliber]

Something I've always wondered with changing wheels is the effect that different widths will have on the setup and handling of the car. Based on my reading from old posts it sounds like this car tends to be pretty sensitive to changes in track width.

That said, I'd like fill in the wheelwells a bit both front and back, but don't want to compromise handling for the sake of appearance. Right now I'm thinking of 8.5x18 ET 35 up front and 9.5x18 ET 26 as pretty close in terms of the look I want (not too aggressive, +13 mm up front and +10 mm in the back) with 245/40 and 275/35 in the back. Probably going to go with Nitto NT05s based on what I've read.

This is probably pretty picky, but can anyone who has made similar changes to their track width comment on how this affects the balance of the car?