I would be inclined to either fit 7's on the front and 8's on the back, or (951) 8's on the front and 9's on the back.
My view is that the tyre width differential for Fuchs on a Carrera should be a nominal 20mm (i.e. 205 on fronts, 225 on rear, or 225 on front, 245 on rear). The two-inch difference between 7's and 9's will cause sidewall distortion on the smaller front rim if 225's are used. This is acceptable, but not optimal.
In my experience/opinion, a larger width differential than 20mm will induce understeer, and the most appropriate rim width combinations are those stated. I think there is a certain kudos associated with the widest 9 inch rim which induces some Fuchs envy....
In general, it is not too difficult (though not cheap!) to get hold of either 8 or 9 inch 911 Fuchs, but the 951 offset 8's are in very short supply, and require significant suspension geometry changes (negative camber) to accomodate them. This can have an impact on tyre life, relevant for a primarily road car. If yours spends as much time on the track, then fine!
I run 7's and 8's on my car, fwiw, and find this to be an ideal combination for a fairly stock car.
