I've bought new winter tires.My original All Seasons ,the stock Conti's have 35k miles on them,95% "straight" highway.My question is do I ride on the stock tires,till they wear out,or do I buy a summer tire next spring.Will a high performance summer tire wear better.Same driving,lets say.

 

If you were satisfied with the performance and wear of the stock Conti's that came with your 15" wheels then you're better off sticking with them. Tirerack.com has them (ask for Alex) at a reasonable price or if you know of other MINI owners in your area you might find some nearly new or used for cheap.

High performance summer tires are not going to wear better because the rubber is softer and the size of the tire is likely to be wider and lower profile than the contis. 35K miles is quite a bit. High performance tires are lucky to get about 20-22K miles.

If you want to stay with the stock size tires there isn't much else to choose from. You change to a wider tire like 195/60-15 or 195/55-15.