I think the 4" is a good choice for the Liberty.......gives it a very neutral balance with most accessory choices. I personally prefer a bit more length and heft out front. The 6" Stealth gives it just a touch more forward roll while static, and a dead solid neautral shot reaction when fired. Extremely dead in the hand at the shot. If I shot my Liberty for 3D I shoot an 8" Stealth Hunter to help a bit more with precise aiming, balance is a bit more forward while static, but at the shot it's very neutral with a bit more forward roll after the initial explosion.
I think anything in the 4"-6" range in a Stealth is a good compliment for the Liberty for any hunting situation.