I need help figuring out which stabilizer would be best for a 1 5/8" tie-rod, 35s, 4.5" lift. I want it to as smooth and soft as possible.

Footnote: I will be installing the Synergy track bar relocate.

 

cheapest thing possible. Don't put a gas charged unit there....pick something that has equal resistance expanding/collapsing. The Teraflex 9550 VSS is an ok option, but you're just as well off sticking with factory. If you're using an aftermarket clamp on the TR, you might have to push the metal bushings out of the SS end to allow the bolt to pass through as the bolt for the clamp may be too large for the bushing.