Just set a 1650 Personal Best, but with a pull buoy?

I've been aiming to achieve an NQT for the 1650 this season (20:33). Came up short the first time I raced in in January @ 20:53. Next race, early March, I went out a bit faster, but blew up on the back half and ended up going 20:59. Gonna take one more crack at it the last weekend before the Spring Nationals entry deadline. Today I was planning to do a fly workout at my normal late-lunch afternoon swim, but then I got a text from my co-worker that he was going to have to go home early, and that I should go to the pool this morning if I wanted to swim. I did so, but I'd already done 30 minutes on the bike trainer earlier in the morning so my legs were a little tired. I didn't have a lot of time, either, so I decided to just jump in cold and do a 1650 TT with a pull buoy (no paddles). I started watching the clock around the 400 mark, and was holding right around 1:16/100. I had to gradually increase the intensity, but I was able to hold that pace for the next 1000. When I got to the 1400 mark, it dawned on me that if I pushed the last 250 a bit, I might actually finish with a personal best. I did push, and I ended up going 20:51....with no block start, and no ability to 6-beat kick the last 50. So, I was simultaneously happy to go a personal best, but also perturbed that I was faster with a pull buoy than without. This certainly wouldn't be the case for any distance 500y or shorter. I think even at 800m/1000y, I'd be faster without the pull buoy. But the evidence that I could pull a 1650 faster than I could swim hit me right between the eyes this morning. So the big question is, how unusual or normal is this? What does it all mean? What is the airspeed of an unladen swallow? Should I give up and go back to middle-distance and sprints?