Core, Lupo, and kr2 pro all use the new kr2 shell. Fits a foot better, is a little less straight tube shaped.
Rampage uses the old kr1 mold.
Completely different boot. I was getting fitted a few weeks ago and tried on the kr2 and the rampage, kr2 felt much better. Ended up getting lupos.
So, if you're deciding on which to buy, whichever feels better. They are very different fitting boots.