Oddly, I had the opposite.

I thought the pace was easy on my Wed. pm ride, and we only pushed really hard on one 2-mile section. We were in a small group that usually rides quite fast, but toward the end we slowed down a bit to wait for one of the guys. So I thought it would be a slow average speed, but Strava says we moved quite well - doing 23 miles at 19.2 mph, and feeling fresh afterward.

The temperatures here were cooler, and I think that made the difference. The same ride in the weather we had until recently would have felt much harder.

http://app.strava.com/rides/20224112