That seems a bit sharp and as if it is now over servo-ed for the weight of car (I am sure that's not a word!) and a servo with a smaller diaphram is required. Alternatively it may be that to much depression from the manifiold is acting upon the servo and it may be possible to restrict this slightly to dull the effort. Possibly a bit of research is required in this area. An American company, MP Power Brakes has quite a helpful web site with regard to such tricky issues.

I would assume that your current tyre size is around the 165 X 14" mark. With 15" X 51/2 72 spoke wires you can go up to 185/70 15's which will improve the situation and cause no problems with rubbing.