Andi and Ellen,
I suggest you go over to F800riders.org and post your question in the F800GS section. There are two wonderful ladies there (only one is really active on the forum, soph9) named Cheryl and Leslie. They did an Alaska trip on borrowed Tiger 800XC's and now they've purchased F800GS's. They're really active long-distance tourers and I'm sure they'd be able to give you some interesting comments and advice.
Good luck on your travels...