Fascinating thread !
I have two JLC Y6b's, one of which is weathered and can be seen in the thread "Layout Vignettes." The other Y6b was redone by Alex Malliae to four cuffs/rev and much more smoke. Having many Legacy locos I feel comfortable doing a comparison Between the JLC Y6b's and Legacy locos with/without whistle steam.
1) The JLC Y6b's are among the top two or three most detailed locos Lionel has ever produced. I am sure the new Legacy version will be no more detailed than the JLC version. For detail, it is fantastic.
2) The JLC version is incredibly smooth and slow. Not quite as smooth and slow as a good Legacy loco, but I just received the new Legacy Cab Forward and it was more herky jerky than any other loco I have received. It went right back.
3) The hooter whistle on the JLC version is as good as any whistle I have ever heard. It does not quill, of course, but it does have a "quilly" hootiness.
4) Smoke on the JLC version is very low (Unless it travels to Alex !)
5) Would I spend $1400 for a Legacy version? Only if I could get 75% of that for one of my others. Unlikely.
I am so happy with my Y6b's I applaud Lionel making a Legacy version. Maybe I should just get one!