An immaculate, restored probably, 100GS PD was on ebay for a long time with an asking price of just under £10K; these are yet another bike that has become over-rated (whatever that means exactly) and are heading for a collectors' garage.
I can still feel your thought process; a few years ago I stepped off a Honda Blackbird that I was riding two up with luggage and that was a superb touring bike; with a passenger and lots of luggage it went even better, with the suspension operating in the mid-range of it's travel and the back tyre digging deep into the road surface.
Now that the shaft drives are under discussion I would throw in the XJ900, Yamaha Diversion which I used to own a few years ago; that bike is vastly under-rated and it has no direct replacement in the current Yam lineup - the FJR1300 appears to use exactly the same shaft final drive bevel box etc but, after that, the FJR is much heavier and bulkier.
The Divy is a fine bike for two up and nowadays it is very affordable if you can find one for sale; there are a few around, but I suspect that owners tend to hang on to good ones.
You could take your pick of all XJ900s on offer for sale with a 3K budget but you won't get far in the BMW market with that same budget; sad, but that is my assessment of second hand asking prices.
But, it is not just about the all up weight of a particular bike; the CoG of the airhead is relatively low and that will compensate for the bulk of a rider/passenger/luggage at a higher position.
Nor, are top end power figures the full picture; for hauling weight up to a particular speed (i.e. acceleration) the torque output is much more relevant - the airheads have this in abundance, as do V twins.

(I can hear the voices in the background referring to "off road" capability, but none of these shaft drive bikes are for off-roading, depending on how you want to define such activity).

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Dave