Whether or not a shoe "tear's your calves up" or not depends on how much more they get you to run up on your forefoot than you're used to. People differ on what the most efficient stance is for them. Bekele and Sihine wear the zoom shift's for 10k. If you're used to running on your forefoot, wearing Kennedy's for a 10k is probably a good idea. A lot of people (particularly really fast ones) would probably find the miler comfortable for 5k's. I've never had the Jasari's, they might be good. Last I checked you could get the Jasari Plus on Eastbay for $50.