The 75k rated tire simply has a higher life expectancy than the 50k mile tire. Is the 75k a better tire? Perhaps, but not necessarily. High performance tires tend to have a lower mileage rating than standard passenger style tires. Look up the two models you are considering at tirerack.com. You will see how they are reviewed and rated.

Trivial at best, since you're never going to get a new tire from either of those warranties: they're prorated based on the mileage you've already used up. The only warranty that actually matters is the road-hazard coverage, and that usually costs extra.

These are brand new tires. I have been there with used tires and had blow outs probably from dry rot. I leaned my mistake with buying used tires.

It is just how long they will guarantee they will last. dont by cheapo china brand tires!