6 hours in FRA....
I would run the gauntlet and get a couple of new EU stamps in my passport...
Clear immigration, store my luggage at the airport storage - prices V reasonable, race downstairs and get the train into Frankfurt Main, out of the station and get a cab across the river to the Old Town, indulge in a great meal at one of the great restaurants available in the Old Town, get a cab back across the mine to the rail station,
take your photo in the same spot as both Flashware and I have now done, out to the airport, get luggage, check onto flight, shower at the lounge and smile at the last 5 or so hours you have just had
thats what I would do....
Mr!
.