@swbca I dropped 15 lbs last year just to see how it impacted my skiing (I was already lean at 185). What I noticed is that it did not impact my PB but my body felt like I could ski nearly every day. I also had a lot less aches throughout the year. I typically ride a 67" ski but getting down to 170 I also tried a 66" since I was starting to feel like the ski was a bit big. Although I liked the way the 66" turned, it was more work behind the boat so I stayed with the 67". My conclusion is that if you are already fit/lean where you are, you will not see much improvement to your PB, however it should allow you to ski more sets throughout the year so in the long run (theoretically) this should improve your skiing in general. Hopefully, year two with my current lower weight will begin to pay off (PB-wise). No matter how lean we are or how much of a spare tire we ski with you still need good technique in order to improve, especially when the line gets short. I think weight is just one part of the entire ski improvement equation IMO.
I also recall listening to a podcast last summer that Marcus had with Will Asher. Will mentioned that he experimented with skiing lighter and heavier and settled somewhere in the middle so for him it might of been where he simply felt the strongest but he did not elaborate.