I can't add to what others have written about sizing, but I will suggest two things:
First, if you visit Anchorage often, maybe do a little searching while you're there and find one you can actually look at and ride.
Second, I do know that there's at least two or three places that rent decent mountain and hybrid bikes in the Anchorage area. I've rented twice from a place downtown called, you guessed it Downtown Bike Rental on, I believe, 2nd ave? Right across the street from Army Navy Surplus, if you know that part of town.
They rent mountain, hybrid, flat bar "road" bikes and regular drop bar road bikes. I've rented flat bar road bikes and most recently a drop bar road bikes. Great experience both times: the bikes were well tuned and worked well.
The other place I know rents moutnain bikes only is Sunshine Sports out on Northern Lights near Spenard (also near the REI and AMH). I haven't rented from them though.
I believe there's one or two othrs.
This might be an alternative if you're looking to ride when your in Anchorage.