I'm riding an 09 Marin Rocky Ridge, Medium. When I got it I found the small just made me feel to hunched up so I went medium. Although fine, would reducing the stem to 50mm rather than the 70mm I'm running now & getting an In-line seatpost make any difference.
If the medium is "fine" why do you want to change things around? Or do you feel a bit stretched out?
Both suggestions will make you less stretched, but I would make one change at a time and see how it affects things. I'd start with the stem.
Where do your saddle rails sit in relation to the seatpost? You might be able to move the saddle forward on the rails a bit to see how that feels before committing to a new seatpost.
I am probably gonna get myself an in-line post as I feel a bit stretched. Was thinking about it while on a ride yesterday. My seat is as far forward on the rails as possible.