5K Training at 100%?

Today was my day to do the 5k at 100%, but it felt more like my day at 80%. My time turned out a little better, but overall I'm a little disappointed with myself. In fairness, I had to stop at three lights and the wind was strong. I give myself a standard 20 seconds off, but it's hard to gauge the loss in momentum. On the first 5K, I actually was slower than when I did the same stretch at "80%." I redeemed my ride (with less wind) on the 4th 5k with a .34 second improvment from my previous time. I consider the 4th 5k one of the hardest. I think I need to go back to doing 5K intervals at 80%, 90%, 100% etc.