I am going to think that any cable lock is going to be just as easy to cut as any other. It comes down to how thick the actual cable is, but that doesn't amount to much because I beleive any smaller end bolt cutter would do the job just fine.

If you don't want to carry the u-lock, you can always just leave it attached tot he bike rack at work. Cable locks are more meant to keep people from simply walking off with your bike. It can probably work if you plan to hop in a store for 5 minutes and back out. Five real minutes and not '5 minutes'. If they wanted to steal your bike, they will take it no matter what security is on it.