Symon
The K60's are nop notch and ride really well. In fact you will hardly notice a difference from road tryes apart from a slight rumble from the from which you get from a TKC anyway. Shawn in Fairbanks reckons they are much better than TKC's for the Dalton and he should know I guess.
Gromit
You can't feel the change when it rolls off the solid center section or at least I can't
The 650 will be OK for Alaska and you'll benefit at the gas station when you are only putting half of what the 1200 are putting in
I was up there in 2008 with a mate on his 650 and he ran with us no problem. We will only be cruising at around 65mph even on the long stretches. As long as you are comfy on it, it will be good but remember there will be 4 or 5 days of around 400 miles.