Is there an Optimal Pull Speed

This morning I noted that at times during my swim I was pulling faster, but making less progress. I slowed down the pace of the stroke and found it more efficient. I didn't change the stroke in any other way and I didn't time myself, but felt like I was making better progress through the water with the slower stroke. Strange. This begs the question, is there an optimal pull speed that works best for the speed the body is traveling through the water? If one's stroke pace exceeds the speed of the water flow, are you defeating yourself by using excessive energy? I'm thinking the right speed is where one catches the water such that you can maximize the pull. But what is that? If you pull too fast, you pull less water and consequently use more energy than you get back in terms of forward momentum. Am I on track to something here or just full or it? Your thoughts dear readers ...