I weigh 190 and ride the 163 sherlock. It's a 5 on burton's flex scale - the custom X, which is their stiffest board is a 7. I read a review the other day that said that it's one of the stiffer non-cambered boards that Burton makes and that beginners or those who prefer a softer board might look elsewhere in the lineup. The reviewer said that the extra stiffness was helpful for larger jumps.
Personally I really look for stiffness in a board for carving groomers and going really fast (where I also want a cambered board). I don't find the need for stiffness in the softer snow, although I'd say the sherlock is in the middle, not a soft board.
I agree completely on the stiffness comments above. This was the review I was going on. Burton Sherlock | The Good Ride
I've been reading a lot of what they've been posting and found the site to be extremely helpful. Also shot an email with some questions into them and got a thoughtful response w/i 24 hours. I wish there were more sites like this where you know the guys have ridden tons of boards to give them a good perspective.