I run a couple of ported Husky 390's and to me they are a far better saw than the 660's as far as balance goes. I know they are not exactly in the same class as the 660 so it's not apples for apples but I sold my modded 660's and kept the Huskys.
Depending on how much you cut you may not notice the weight increase on the 390XP's over the 372XP's as they are superbly balanced (I can't notice much difference). I however DID notice the extra weight on the 660's, not overall mass but the fact that to me they balanced extremely poorly. In fact they were nose heavy with 32" bars whereas the 390's are not.
I am not questioning the 660's toughness, reliability, and popularity but I've said it before here - how many people in a felling situation have spent time on both 660's
AND the 390XP's? If simply dropping into logs then the 660 has the edge in my opinion but not by much.
Each to their own but I can't believe that if people had used both saws they would pick the 660 for balance and feel alone.
Dealer support and the availability of cheap parts is another matter. There are very few aftermarket parts for a 390XP unlike the Stihls.
You already have bars etc to suit Huskys so that's something to consider too. A 390XP will do everything a 372XP will plus more.
I'm ducking for cover as we speak
but I can't help but think the Stihl 066/660's popularity is a 50/50 split between the "my Pappy ran a Stihl as did my Pappy's Pappy" factor and because it's just a tough old saw. Many people that jump on the 660 bandwagon have never spent much time on any other saw.