Mr.X I think you must focus on what you really need. For what I read, I lean to think that you need a 75/77, but lets' talk about it.
Now what are YOU looking for?
1) Is it a second gun to alternate with your primary 90cm for low viz days?
2) OR is it a bit shorter MAIN gun since your 90 has shown to be too long most of the times?
In any case consider that the overall length of an 82/85 gun (considering also the shaft length) is just 5 centimeters shorter than a 90, so if you switch to an 82/85 you won't gain much, just 5 centimeters, for the visibility issue, while the shooting power and range will be inferior.
If I were in you fins I'd get a 75/77 and bring on always two guns, one clipped to your float, to alternate them according to visibility, terrain and tasks. Me I always bring on 3 (a 106, a 77 and a 60), which is probably not necessary in England (no pelagics and no holed-in fish). But anyway, you have that damn visibility issue, don't you? Believe me, bringing two guns, once you get used to it, is not annoying as you could think.
It's more annoying to argue with wife or work boss for taking a day off, travel to the sea, get dressed, get wet, and then finally realize that your only gun is too long/too short for the situation...