For what it's worth, I really really really love my PowerGrip straps.
Here I am on a very cold day, keeping my feet toasty warm in my insulated hiking shoes, with heavy wool socks, and my PowerGrip straps adjusted to accomodate my bigger winter boots. It's very hard to jam clunky winter boots into any clips, but no problem with my straps at all.
http://harmonias.com/bikes/L_riding1DSC02460.jpg
(That's just a water bottle cage showing on the frame above my foot, by the way)
I have no problem pulling up to get upstroke power when my straps are adjusted right. Nice and snug, but super easy to get in and out of quickly during unexpected stops.
That's my two cents.