would love to see some pics of the Fuchs.
you will want to go with the steel arms. i am running late ali's with 8.5ET48 wheels and it fills out my 3" CCC fenders perfectly. with 10ET5 you are adding another 50+mm in track width. i don't know anyone making 5" fenders.
plus i believe you can get 944NA brakes under 15's. i am pretty sure 993, 951, etc won't fit in 15's. but hopefully someone else can confirm.