DIN is also dependent on bootsole length, as someone who actually knows what they are talking about already said. i know guys that are 6'7, 200 some pounds that ride a din lower than me (6', 160lbs) because their foot is so much bigger than mine. the bigger your boot, the less torque it takes from the ski, since the toe and heel are closer to the tip and tail of the boot. you can think of it in terms of swingweight. when you hold a ski dead center, its easy to swing. when you hold it at the tail, its harder to swing. smaller boots are like holding the ski at the tail, since with a smaller boot, you have more tip and tail to work with on the ski, if that makes any sense.  if the shop uses the DIN chart to tell you that you should be riding at 8-9, then base your decision off that. if you're riding a look/rossi binding, go with what they say for the toe, and one higher on the heel. for salomons, go one higher in the toe, two in the heel. that's what i've found to work out pretty well for park riding. if you're riding a pair of markers, then god help your knees...