In the ITU worlds, my bike IF was 89% and run IF was 97%. On that one, which was pretty hilly and technical bike course, my average speed was 36.5kph.
In comparison, at the Zyterm triathlon, my average speed was 42kph with an IF of 85%.
My bike split in Zyterm was 8m30s quicker than the ITU, even though IF was lower. So even with weight loss, I think that Eastbourne will be tough to get a PB
The first Tri where I did the bike sub 1hr (2016) was Dorney lake
Totally flat bike, totally flat run (on that occasion the swim was cancelled due to algae). I just looked at my result, and the bike looked a little short as I averaged 37.5kph, however, At the time I weighed around 78kg, FTP was around 255, 10k pb was 44mins, and I had never done a HIM, or even run a HM.
Dorney should be good for a PB as Transition is right right on the swim exit with no distance to the bike or run course. Its as boring as hell, but no cars to worry about, and if I remember well, just one tight chicane on each of the 8 laps