[422flat6]

185/70-15 or 195/65-15 are the sizes that will maintain speedometer accuracy. If you want a summer performance tire your choices are limited to the Pirelli P6000 or the vintage reproduction tires like Avon CR6ZZ, Michelin XWX, Pirelli CN36, Vredestein etc. I just put P6000s on my narrow fender 72 but will have to reserve judgement until I have some more miles on them. The Avons seem to have a big fanbase with the Early S Registry guys.

If you are ok with running less sticky all season tires there are several choices available in 195/65-15.

If you want the latest technology in summer performance tires (Bridgestone RE71R, Dunlop Star Spec) you have to use 205/50-15 which are very short and look like golf cart tires on a 911 (in my opinion) or go to 16" wheels. 205/55-16 will maintain speedometer accuracy and the latest tech tires are available in that size... for now.

Yokohama S-drive is available in 205/55-15 which will fit, is a decent summer performance tire and will have less effect on gearing/speedo than a 205/50-15 would, but it is shorter than stock. So compromises all around with this tire but maybe it's an option for you.

Bridgestone RE760 Sport is available in 205/60-15 which won't affect the speedo but is not sold in the USA. You can drive to Mexico and bring a set back depending on your Spanish skills and risk tolerance. I don't think these are DOT certified but I'm not 100% sure on that.

Based on my very recent research, that is the state of 15" performance tires for narrow fender 911s as of August 2016.