If you're heavy AND big, you'll likely find the XU ungainly, or ...... it will find you ungainly. I'm 6'4", 235 and found it had plenny power on the redwood back roads of Scotts Valley, but my legs were totally in the way. Never tried it on the highway. If you're more compact, an XU may work for you.
The range bump for 2012 was significant, and I can't imagine they'll pull-off any similar % gains for 2013?
I imagine there'll be i
Some improvements in range and efficiency, but I expect greater changes in cosmetics, fit and finish. Just my guesses though.
Buy as much pack as you can afford(or maybe a little more
and I don't think you'd regret it.
BTW; The 2012 'S' and 'DS' packs are rated for about 310k miles(TO 80%); potentially a lifetime or two of riding.
Also am PM'ing you.