Love the zoom fly, this coming from a long time clifton user.... Clifton 4 is heavier, stiffer and overall a "slower" shoe. I had a pair for a week and sent them back. The zoom fly is good for me at all paces from 10k to marathon to easy days. I've had them since release, raced a 1/2, paced a full, and a ton of training miles....still enjoy them. The only, only gripe is the heel counter is high and stiff, especially the first 20 or so miles...I needed to switch to 1/4 high socks to avoid high heel blisters. I also have the vapor fly, which are just amazing so far, plan on racing in them at Chicago. Gotta love running warehouse if you're unsure....can always return/exchange if you don't like them.