Replying to How important is boot flex?

I just bought a whole bunch of new equipment for the upcoming season minus new boots thinking mine were fine. The flex rating is 90 and apparently that's not good enough. Since I don't wanna shill out $600 on new boots I wanted to know if this is going to seriously impede my skiing ability or chances are I won't notice?

For reference I'm 6'0 and 150lbs and would classify myself as an advanced all mountain skier.

Thanks