Thank goodness, someone's posted a sensible answer. Thanks Pete. Because of the torque increase you'll find your changing up sooner and improving mpg.
Regardless of what pistons you run you will get detonation, my old 7.5:1 would detonate something chronic. On my 9.2:1's I rounded all the corners off and it doesn't pink for anything.
There is a lot to be said for high compression, especially as BSA balanced the cranks with HC pistons, after trying both, I would never go back to LC pistons.
I would recommend only using premium grade fuels and not over retarding the engine.
Sorry Adam, 7.5:1 are good pistons, just not for me or what I want to do with the bike.
If we put these questions forward, it might help choose.
1) do you have a dodgy leg? Low comp is easy to start!
2) are you going to be doing big mileages?
3) what sort of speeds do you expect to ride at? 50-60 mph maximum, use LC, if your looking for the Ton, and want better acceleration, fit the HC pistons.