I am becoming frustrated by the lack of tire options in the stock 195/65R14 or 205/60R14 size for my 1991 318i. For autocross, I wish to upgrade to "Extremely High" Performance Summer tires. I am thinking of buying a set of 16" rims which has a huge number of tires available. The correct size would be 205/50-16, but there are even more tires available in 205/55-16 (including the exalted Bridgestone Potenza RE-11s). 205/50-16 typically make about 865 revolutions per mile and 205/55-16 typically make about 835 revolutions per mile. This is a 4% reduction. Is this significant? Would I notice it in my performance?