I'm 5'6" on a good day.. 28" inseam... had an R1200GSA for 4 yrs, 36K miles and up to AK too....
You'll want the 1200 for a few reasons... no chain to maintain (yes final drive horror stories.. all anecdotal).
1200 will give you better power... better wind protection... won't get pushed by sidewind as much... better overall comfort... larger alternator for electrical gear...
29" inseam w/a low seat, you'll be fine.
Just find a lightly used 1200GS... there are lots of them out there for the same price as a new 700/800GS.
"I've never had a bike ask me if I'm going to be inside riding my wife all day"
1999 BMW R1200C & 2007 BMW R1200S
Past loves: 2008 R1200GSA/2001 R1200CLC & Phoenix /2005 F650GS/2002 R6/1973 R50/5 Toaster