They're extremely nice to run in. I think the nicest Vibram for running so far. Nicer than the KSO or the Bikila.
My goal for my speed work is to win a 5k for my age group next year. The fellow who won the age group under mine this year ran 6-minute miles in KSOs.
So, taking Gordon Pirie's advice, I'm first trying to progress up to running my target speed, and then trying to extend that speed to the target distance. I did this a few years ago with some success, but was sand-bagged by surgery and plantar warts, and training hit the wall.
Hopefully it will go more smoothly this time, and even though I'm no longer being chased by a man with a knife, I feel pretty motivated.