That dreaded tire question, Mahle's Options

[tracks914]

Before I go out and sink $500 on new tires, I thought I would ask the question. I do recall some rims and suspension combinations don't work and that the stock tire size is about 5-10 MPH off @ 100mph but...what can I expect with....
Here is what I have;
1972 914 1.7 stock suspension.
1973? Mahle 914 361 015 00 rims
I would like to put P205 15R 60 Dunlop SR tires on the car.
I have read that this tire size is the largest I can put on without the tire rubbing/touching and yet the speedometer might be more accurate because of the reduced tire circumference.

Tx
Doug