That's kinda like asking what is the best way to have fun on a date with a really ugly woman.
Most of us, if we knew, wouldn't admit it.8=)
We all draw the line at different places, and for me it's at around 600 pounds. Somewhere around there a bike stops being a motorcycle and becomes a two-wheeled car or truck.
When a major part of the equation becomes, How much will it carry, or tow, I'll opt for four wheels over two. Autos carry or tow far more efficiently, and even handle and perform better than a lot of touring bikes.
Maybe someday I'll get old enough or my waistline will get big enough that tourers will make sense to me. God, I hope not!
The BMW K 1200 you mentioned seems to be getting a lot of support from the mag. writers. I do know that the current Wing is being replaced with a new model; supposed to be 1800cc. A warped, speed-crazy dude like me would check out the BMW, then if I didn't like that, wait for the new G. Wing.