What are people replacing their stock D208s with? The rear on my XL1200CX is pretty worn on the middle (the perils of buying a demo) and the middle tread bars are going to appear soon enough (@ 8200km). I hear anecdotally the factory Sportster tyres are "very soft", is that accurate? 

well, I have always liked Avon Venoms  & think they look better too.

Cool, I will check them out and see if I can find a supplier closeby. In the meantime I have googled and found a few forum users reporting Pirelli Scorpion Trail II and Dunlop Trailsmarts perform better than the OEM Dunlops. These are adventure touring tyres designed mainly for on (but also off) road. I'm a bit surprised, that Dunlop can't make a tyre dedicated to road use FOR Harley Davidson that's outperformed by adv/tourer ones... For me the factory GT502s (yes I was wrong, google said D208 but the bike has 502s on it) are good but having A. never ridden a Harley before and B. not ridden my bike with any other tyres, don't know how good they are compared to what else is out there.

Pirelli Night Dragons, Metzeler M888 (or m880), Avon Cobra's & Dunlop Elites are all good tyres that I have used, I usually buy which one that is on sale at the time a tyre is needed, so a few more options for you to consider

+1 on the Avon’s. Good mileage and stick like shit to a blanket.

The avons are excellent but cost a bit.

I'm a huge fan of shinko 777 but they don't last long. Best dry weather tyre I've tried.

Ive just ordered white wall 777’s for my sporty project, only heard good things. Usually run 888 marathons or Avon cobras on my Dyna, both excellent too