If that's the stock 91-92 wheel that's a 16x7, I wouldn't go wider than the stock 225/50/16. If they're Mk4 16/17x8, I'd stick with 245 widths or lower. I'm currently running 255/40/17 on 17x8 Mk4 TT wheels, and the sidewall is squishy as all hell. Good way to think of it is that you want your sidewalls to be somewhat 'square' with the wheel. If they flare out too much, you're not using the extra grip that you want out of the wider wheel.
I learned my lesson.
Also, there's a wheel/tire fitment thread stickied at the top of the General Mk3 section (where you posted this thread) that should be of great use to you.