What bindings do you have? I wont be able to tell you anything until I know. From experience though I can only tell you to bring then to your local shop. Im a ski tech at mine and these questions cant be answered until the boots are measured up. Even though manufacturers will give a BSL they are not always accurate, for example my new Dead Money's have a supposed BSL of 325mm, but measure longer than my SPK's that had a 327mm BSL.
man i wish my currency rhymed with boner... -the.cheat
Nobody will believe him when he tells the cops you just randomly started pissing everywhere , but his fingerprints will be all over your dick so he is screwed
12 hours later and I'm all stitched up at the University hospital....vision unaffected. And that's how I got stabbed in the eye by a hooker.- Barefootin_Fiend
The look PX 12 has a length adjustment of 45mm, so you should be fine? Just reading this off their website. Im not a ski tech. But most bindings will allow movement to fit a change in boot size, by one or two sizes.
your bindings will move to adjust to the new boot. but if you mount true center with the smaller boot and move the heel piece for the larger boot you will no longer be centered. you will be a little bit back. your 3.5mm wont make a big difference but moving multiple sizes will screw things up big time.