I'm 6'1 and 176 and most of my all mountain boards are 159, depends on the conditions you ride in. The longer board will be more stable at speed and better in powder, the shorter slightly more maneuverable.
I'm about 180 and have a 158 Revolver (wide version of the evo). Unless your definition of all mt riding is playing around on mellow groomers then I'd look elsewhere. To me the evo is a park board that isn't terrible for cruising around the rest of the mt, but by no means is it an all mt ride.