I have a similar setup to what you have. 17x7et55 wheels up front 205-40-17 and 17x8.5" wheel et50 with a 245-45-17 tire and a 1" spacer on 5x130 drums. I use a 1 1/4" wider fender, about 32mm. Believe it or not, that width fender brings the whole car into square, as the front fenders are wider than the rear on a Super Beetle. So, all 4 of my fenders are in line with eachother. You really have to look to notice that they are wider.
However, you could use 17x7 et55 wheels in the rear with the stock fenders, but I prefer the staggered setup. I just love big meats out back
