I think a lot is down to the individual, I am quite fussy and like to be able to swing on the throttle a fair bit, and even two-up I like to be able to use the grunt / power out of bends.
Most bikes I have owned have struggled two-up on OE suspension, some where better than others, but most would wallow a bit on faster bends and run wide if winding it on fairly hard out of turns as the back of the bike sank under the power and weight.
Most bikes I found where much better if I rode more steadily (which two-up I do to a degree) but the fact I could not ride how I wanted at times annoyed me enough to go and spend some dosh on better suspension.
My Gen1 S10 was no exception and also suffered very badly with ground clearance, on the stock suspension solo with an extra couple of lines on the pre-load I did not notice a ground clearance issue on the (Crap) UK roads near me, two-up with full pre-load it was not hard to find the limit of ground clearance, with two people and luggage it was frustratingly easy to run out of clearance even on what I considered a steady touring pace.
I always do a loaded test run on a new bike, just a weekend away, on the S10 this convinced me I needed a new shock before any long tours.
The Mrs getting her own bike worked out very well for us as she is a good confident rider and can maintain a decent touring pace, we can actually do more miles in a day now as we both find it more comfortable not sharing a bike so stop less and her solo pace is as good or better than our two-up pace was - and I can occasionally wind it right up without the kidney punches.
