Rolf
I really like the 8:1 simply because you can't oversheet! I think I'm putting on enough tension to pull the sail into it's designed shape, I say this because I get to a point where it's practically impossible to pull any more sheet in, if I do then surely I'm going beyond the designed shape and just pulling the nuts of the the leach which in turn must be having an adverse affect on other areas of the sail shape! I don't really suffer muscle wise whilst sailing with what I consider to be adequate main sheet tension it's just my hands ache for a couple of days after due to them being crushed. I'm using Harken blocks and a 8mm tapered Dyneema sheet which are washed out in fresh water at least once a month so I don't think I have a friction issue and my Gill gloves aren't in too bad a condition.
I might just have to consider adding some purchases and be careful when the adrenalin starts pumping.