I own an S6-L - I'm around your height and find it fine (seatpost fully extended, pentaclip near the top of the post too).
The 6 speed's gearing goes pretty low - I've not found a hill it couldn't handle yet (otoh, I've not hurled it at Mow Cop, or anything). The derailleur is finicky, and ime, needs to be kept clean to work at its best.
Do get a luggage block, and if you can, a bag - I have the C-Bag, and it's a brilliant way to carry luggage. Don't be tempted to get one without mudguards - the bike is so low to the ground that it gets really dirty - I dread to think what the state of mine would be without them.
In hindsight, I sort of wish I'd got a rack (more for the ease of wheeling the bike around than for luggage), and sprung for a Racing Green one, but hey ho.
Oh yes, as others have said, go to a dealer and try some. I bought mine from Harry Hall, and they were brilliant about letting me try the bike out, do some test folds in the shop &c
