1.seat height which is lower ?as I am 5/5
What is inseam?
Either bike will need to be lowered and get some height from your boots for stability. Alaska mud in construction zones is nasty squirmy stuff and there are sections where many riders need to paddle due to rocks,
The 650 weighs less to start yet carries the same load.
You might like the extra power gettng to Alaska but my 650 had no issue at 75-85 all across the plains asnd there was more left.,
2.Better 2 up?
More oomph but see above.
3.80/20 More Highway!
I'd strongly suggest 50/50 K60s or Mitas 7 for the trip
4. Sufficient Power I like to cruise at higher speeds 70limit 80-90
The 650 will do those speeds but into a headwind uphill there will be less available but that's what gears are for.
5.Gas tank size
More concern is range and the 650 does better
Personally the lighter weight, longer range far outweighs the power for the height challenged rider ( I am as well )
The 650 is 41 lb lighter and a lower seat height by .6" as a start point.
With the new motor, traction control and other features I'd be recommending the 650 for you - lowered and you with lifted boots and careful with your luggage loading to get C of G as low as possible..
Here's a recent Alaska report
Whew! Central Fl to Key West, Fl to Prudhoe Bay, Alaska and Back. Just Finished! | Adventure Rider
Welcome - enjoy.