I found the little paper tag with all the info on it for my garage door springs. It turns out they are an unmatched pair. The left one is 27 1/4 inches long. The right one is 30 1/4 long. The left one has a wire diameter of 0.234, the right one is 0.243. That means that the left garage door spring is good for about 1,000 cycles less then the right spring. 15,000 and 16,000 cycles estimated based on the spring info. These springs were installed 09/26/1985... Ok, they sure did their job.
I'm replacing them with a matched pair of springs that are 35 1/4 inch long, and are rated for approximately 28,000 duty cycles. 122 bucks all up. Not bad at all. I could spend 200 + 20ish shipping and get the ones rated for 141,000 duty cycles. Only, those would probably last longer then the house will be standing...