Mondo, I'm 165 lbs, roughly your age, found the AC4 170 to be better in bumps and trees, 177 better in the open and in deeper chop. Both were very stable, excellent on hardpack/ice/crud. Agree with W that 163 would work fine, think it would be very quick, easy, might have a speed limit. Depends on how you ski, where.
For me, the piston has a mild effect of stiffening/damping the front of the ski, don't believe they are scaled to ski length, so shorter skis will show a little more effect. Which is good if you're going for the 163.