I also think that pleasure is an issue. For me it's much more fun to ride a bigish powerful bike, 50.000 km on a single cylinder bike doesn't sound like my kind of fun - but people are different.

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With much less experience than many of the contributors, I am trying a approach with this type of pleasure in mind.
I have a 2006 1200GSA that I took half way around Australia with 55kgs worth of gear including hard panniers. The few times I went off road were scary, based on the weight and my lack of experience.
Using the expertise of the Ultralight community (backpackers/cyclists/others on the Hubb), I have reduced my gear to under 20kgs. I have replaced the battery, replaced the rear rack and rear seat with a plate and gone for Giant Loop soft luggage, also replaced the stock muffler. This reduced my weight by 22kgs before gear! All up saving of 44kgs!
I have sufficient gear to do a RTW trip (minus food and water) and my bike is around the standard weight for a GSA of 260kgs fully packed. While that is still a heavy bike, I am trialling it with that setup around some harsh Australian off-road in The Kimberley (WA). I am not in an enduro race and I don't need to push myself to extremes, but I do enjoy some fun off road and so far I have traversed deep and sometimes wet red sand, knee deep creek crossings, corrugated and stoney roads and the bike has handled it all easily. I can happily skip across some gnarly roads at 100km/h with ease. Yes I've come off but a standard GSA is not that heavy to pick up for me, so no big deal so far.
I rode 9000kms on tarmac to get here and the same bike is handling this terrain, all with comfort, tons of power and ease.
I also have a Yamaha XT600 that I used to regain my riding skills on. Great bike, but would not have considered it for a minute to do what I have done on the GSA. It was hard work to ride over 100km/h on the highway and never felt as stable as the GSA in any conditions. That was without gear.
In summary, A large bike with very light gear is my choice. I'm sure the 800GS would be equally capable with light gear and significantly less total weight than the 1200.
Question to all: How many of you weigh all your gear and know exactly the weight you are carrying?