Truth be told, you won't find the "ultimate" upland 16b gun for under $4k. That said, and given your paramater of a steady diet of Rem blacks and gp's, suggests to me that you should be thinking of a new AYA 4/53, AOC Uggie, or something similar. I just bought a new Uggie 16 and it fits your parameters exactly. Very lively balance/handling/light weight/straight stock and stout action/barrels capable of steady diets of hot factory ammo don't seem to be the domain of used guns, although I'm sure many will disagree with me.

Good luck!

Imagination is everything. - Einstein