Smaller, lighter
Thank you Olestra. Yes you are correct, also the smaller OD with the lower profile tires enables more practical use of 5th gear at max power, at least at the end of the straight at Lime Rock. 5th was too high and now it is perfect for about 125mph and 4th works for the turn...
Correction/details
My rims are 18" not 17". Kosei K1 TS, 18x7.5, 52.5 offset, weight 16 lbs. Tires for road racing track G-Force P225/40ZR18. Works very well, front pressure 41, rear 38 hot.
It will cost you
My five year old batteries on this redundant system have started to fail. Also had to replace a control unit of some kind. Very expensive and not covered by extended warranty as "batteries" are not covered!
17" rims with the right offset and tires are a great improvement. Car is lower, unsprung weight is less, ratios are more usable. (155 MPH in 6th is not much use is it?) Terrific performance in 4th and 5th. Handling is improved. These are my findings, how about yours?