I'm another 5'7", 30" inseam F800 GS rider, and I've had my '12 800GS Trophy for almost a year and 11,000 miles and absolutely love it. I did have several close calls and a few actual tip-overs the first couple of months and finally bought the BMW low seat and crash bars - both were worth wile investments. While I find the low seat comfortable, I'm getting ready to go back to the stock seat that came with the bike. Over the past year as I've become more comfortable with the bike, my balance has improved and I've learned to plan ahead where I'll stop and also sliding forward on the seat and to the side in order to plant one foot firmly on the ground.
I hope this helps, don't let an inch or two in seat height stop you from riding a great bike or getting out there and exploring!