18:57.1
I was planning to try just to shave a bit off the old PB (19:32.1 or thereabouts) which the 1:56 I mentioned would have achieved. But I overdid the first few pulls and found myself at around 1:53 then found it difficult to ease off. So I just stuck with it, eventually settling down to 1:53-1:54. I didn't have a hrm on, I think that would have just scared me. I wasn't sure I would be able to hold that pace but by half way I'd an average of 1:53.8 and I knew that even if I eased off to 2:00 for the second half it'd still be a PB. From 2000m to go I was hanging on a bit and slowed to 1:55 for a while but managed to up the pace from about 500m and got below 1:50 at the end. Average pace ended up at 1:53.7.
Stomach felt a bit funny at times, but ok as soon as I stopped and I recovered quickly. Went and did nearly an hour's abs & core routine, and then 500m slightly subdued swimming.
Still not as fast as Andy's PB afaik.