Today I was riding with a guy that looked to know what he was doing on a bike, but wasn't pressing it. I caught him and then passed him, but as some point decided it would be better to pace with him. We chatted, I pedaled harder than normal. When I got home I found that I bettered my recent lap times of Prospect Park by 1.4mph. Even better, it didn't feel like a struggle. RidewithGPS says I did a 19.4mph lap today when the best I've been averaging has been 18. Last year I was able to easily do 19+, sometimes even 20, but was in better shape. Mind you, this was casual fast riding, not all out. The fastest I ever recorded myself on a lap is 21.3mph, but that was an all out effort. The loop is 3.38 miles with a short 4% or so hill at one point and of course an equivalent 4% downhill on the other side. There are also others in the park so you do have to be a bit cautious.
I was watching my HR going up and it wasn't as high as it had been lately, so maybe I'm getting better.