Like +15 to +25. But good luck finding that. I have the same sport rear fenders. I run a 30mm rear spacer and 3mm front spacer (for my 20x11 square setup) and keep them on with the 18x8.5 +48 offset E53 winter wheel setup. It still is very sunken-in but looks acceptable.
P.S. E53 wheels don’t fit you less you bore the hub bores 1.5mm (which I did).