Hey there. I'm sure you've seen my thread as it is the only other one on the body forum. I have 8x15 ET-25 and I just received the 7cm widened inner and outer rear fenders. They fit perfectly. Any smaller and my wheels and tires would not tuck under the fender. Tires are 225/50/15.
Not sure exactly how much track is increased with the aluminum arms, but seems like your wheels will be 67mm narrower than mine.
Here is a handy calculator to compare different wheels.
http://www.1010tires.com/WheelOffsetCalculator.asp