I kinda hope that the discussion in this thread gets stickied or put under a generally sticky. The information here is certainly very usefull.
A brief story on board size...
I am 5'10" , 208 , size 11 boot , and 98% of the time I spend out of the park.
I had only ridden a handful of times (varying lengths) before finding a 167cm Burton Baron on the side of the road about 3 years ago. As soon as nobody claimed that board, I started going riding alot (~20 first season, ~50 trips last year, ~30 this year). From barely barely being able to link turns to feeling confident on hardest inbounds east coast runs, I've learned entirely on that long, wide, pretty stiff board. Well, I bought a new board, a Rome Slash 158cm, a few weeks ago. The trip prior to the new board getting here, I tore the meniscus in my knee. I've been on the new board twice since then and have been limited to smooth carving as the bumps, jumps, and spins hurt like hell. This type of riding is where the longer, stiffer board should shine, but I could'nt be happier with the choice to buy a shorter, flexier board (I am approaching the limit of it's weight range). The Slash is plenty stable at speed, changes direction much faster, holds an edge well, spins so much better (I had to try it once), is more forgiving on landings (had to try that too), and just generally feels like a great ride. It took me maybe one run to get used to the way it felt. And the last time I was out, I carved a masterpiece on an inch of fresh snow, nice arcs with little gaps of nothing in the transitions, lovely. In other words, don't worry about getting a bit shorter in length. This is one area where the extra inches arent always better.
I've already decided to make the old board a splitboard, it'll be reserved for deep powder days and backcountry use only.