I have K2 Thraxis since last year and I am enjoying. It is very stiff when compared with my older salomon faction (that's the only two models that I had riden). In spite of K2 Thraxis be a stiffer boot I found it very confortable, and when riding they seem to be even more confortable than my salomons.
I just hope that my Thraxis will match well with my new Heritage.
So if you want to keep with k2 and you don't mind in getting a stiffer boot in my personal opinion Thraxis is a very good boot their down side is that you will take sometime until discover the correct amount of strenght that the BOA will apply. At the beginning I tight all at maximum and I hurt my ankles. Now I tight the liner at max without stopping the circulation in order to avoid heel rise. Then I tight the lower Boa at a medium strenght and in the end I tight the Upper Boa just a little bit until it stop beeing loose. I continue this way until today and I am satisfied.