I've just ridden the LHT down to Istanbul, and did 100-150km every single day of July (total 3,600km). That's the ball-park I'm in, long days over sometimes rough (Central Europe) roads. At that distance the odd kg makes not much difference, it's more about comfort.
When I push hard on the (LHT) pedals I can make the chainring/chain touch the front mech (chain on the middle ring), which I assume is the square-taper BB flexing. I've never been concious (or smart enough?) to know if the frame flexes. I've also done 9/10 hour days on the LHT and not felt bad at all, so I guess 'stiffness' isn't a problem for me.
I've only ever used 28mm on the LHT, and don't see any reason I'd change that. I do like the idea of a rear disc brake though, on the CT, which is possibly the thing that will sway the decision.
The idea of a single/versatile bike appeals, and with a lighter set of wheels the CT might actually be the one. I am very interesting in doing the
http://www.transcontinentalrace.com/ next year, and would love to do it with an 'inappropriate' bike (most/all are on carbon or aluminium).
thanks