You have a sturdy rig there and at 11 stone 7 (161 lbs for the Americans on here) you are pretty light so the bike could probably take a 100lbs more. However, I think you are asking the question from the wrong perspective. You should be asking how light is a light load. In my experience anything over 50lbs of gear (not including the bike) is just stupid and people haven't thought about their gear in any sensible manner. Some thought should get you to between 30 and 40lbs, a bit more radical approach and some ultralight gear will get you to below 30lbs and you are at the hardcore ultralight end of things if you can go sub 20lbs on an unsupported tour.