Yep, for me the Skys are good for threshold reps / anything submaximal in the 3:35-3:10/km range but they have an unstable heel and bottom out with a slap if landing hard like when running downhill. Magic speed 3s are firmer with a solid heel, a little lower in the front and good for zone 5 high-cadence speed; easier to keep your footing when digging deep. Skys are faster but speeds are more fun. Neither is very forgiving over long distance - Skys punish low foot arches and speeds punish the knees (relative to cushy super shoes).