Replying to Looking for Boots

Hi,
I'm 19, I would consider myself an intermediate/ advanced skier. I hopped over from snowboarding (of 6 years) last year and have loved it. I'm looking for a pair of boots, size 25.5. I have been reading around a lot about intermediate/advanced skiers should look for about 100 flex but (having not owned a pair of ski boots) I can say that it makes sense by the charts but, from an athletic perspective, I feel I would need stiffer boots. I like to play sports aggressively and skiing isn't different and so I'm a little torn as far as that goes being: 5' 9", 140 pounds (working out a lot so, I'll be 150 at least by ski season) what stiffness of boot I would thrive in. I look to be pushing myself a lot this season, going on/off-piste, off trails, steeps, all of it. And I want it to be able to keep up with my aggression (not necessarily a super speed demon but, fast nonetheless) so any advice or boots available would be appreciated! Thanks :)