I had a 'Nasville' on my '76 S.G. - and It's extra mass did not affect sustain or feel enough for me to ever notice , on that guitar. As Ratrod said though, it was very 'solid' feeling - and a good plam rest.
The thing I wanted to sign in and mention ( forgive me if this sounds unintentionally patronising ) - is that when I had the same problem as you on another guitar - I noticed that I had the low 'E' saddle screwed back hard against the bridge. BUT I could get an extra few Millimeters of movement from putting the saddle(s) in backwards : that is to say that the lower mass of the saddle was against the back of it's recess, but the 'blade' on which the string sat, was facing the nut instead of the tailpiece. I removed and replaced ( reversed ) the bottom 3 saddles - and all was well.
Just a thought, which I though would be better being dismissed as irrelevent - rather thatn not being mentioned at all .. :)