should be fine - boot sole length would only be a max of 1-2mm different, if not the same..you can generally vary almost a whole size in boots without having to remount (not suggested, but possible)
haha, me and my cousin use the same skis for summer sessions, and my boots are 344 and his are 327, without moving the binding at all. You can move the binding alot, but you might not be where you want on the ski.
Yeah I'm aware you can, I've used my rents skis and both their feet are completely different from mine. I've always just slid the heel piece back/forward.
Although when I got my new boots my shop said I'd have to remount them, even though I could've easily slid my toe piece back 1-2cm,but I guess it's better to fit snug.