Phil, that equates to skies i am seriously jealous of! on the envy scale of one to 5 - it would be a 3.5?
When I say the mag's are a personal guide for me, if I was to see a southern latitudes specific bortle scale, i would envisage the two madge's and the two mega globs would figure largely. Because they are diffuse objects first, and in the case of the mag's VERY LARGE diffuse objects, which makes them ideal, i would think, for true visual 'unaided eye' quick rough estimations. The level of stucture and detail you see in the SMC and the LMC varies a lot, with conditions and the site, as you all know. At really dark skies, to us, the LMC takes on a more rectangular solid barred stucture and the apparent 3Dness can be wild of course with both of them at truly dark skies when they are crossing the meridian particularly - I would include the 3D factor in any scale too. Also with the SMC being around mag 3 but very diffuse and large - i find it diffucult too see at all naked eye in most suburban situations, if at all most times. i would say if you can easily see the SMC low or at nadir for mid latitudes you would have at least 6th mag, or close to, skies. With some obs you have to state the LM in the same area of the sky you observed the object in, and thats what really matters in most cases i guess.
Kearn