Have a 2014 CS, MT, 19" tires. I've used the original equipment Goodyear Eagle F1's on my last replacements, but I'm wondering about other choices. Are the Porsche N-spec tires really necessary? My mechanic is high on Continental tires in general and I see a Continental ExtremeContact Sport on Tire Rack. Any experience with those? I'll be replacing only the front tires...ok to mix brands (rear are still the Goodyear Eagle F1's)? Appreciate any recommendations as well as experiences on longevity. Thanks!