Here you go. This is entirely on roads, and starts near Hitchin, ending near Berkhampstead and according to bikehike is AAA at 15.32m per 100km. It’s entirely in Herts.
I actually had a higher climb ratio at 50km, then it dropped as I headed west from near Harpenden to reach the next hilly sections I know. So you could do a 100km out and back from near Hitchin and no further west than Harpenden that looks to be AAA.
I’ve saved the track and might have a look when on PC , on my OS mapping, as I’m sure there are optimisations to minimise flattish sections. This was done tapping away on my iPad based on what I know on the ground.
It’s close enough for me to do a test run on, on an out and back. I have a barometric GPS which should give some clue as to how good the bike hike elevation figure is.