Welcome from Mass. You would be surprised what little gain you actually get from the added length. Sure, you may get + 150 FPS from 16” to 20”, or + 150fps from 20” to 24”, but at the cost of several pounds at the end of the barrel where you’ll feel it most. You state it’s a range toy so that may not matter.
To address recoil a brake and a heavy buffer will manage ghat much better than extra inches on your barrel length.
ill admit you lost me on the bayonet for a rifle you have no intention on wielding other than bench shooting or “anywhere someone wants to take a long shot”. I get it if you want it for looks, nothing wrong with that if it’s what you like. But there’s no practical reason for what you described your intentions for the rifle.
A fully loaded rifle rifle with a 20” barrel and magnified optics will be a 13-15 lb rifle. Add more length to your barrel or handguard and it’s more lbs. Just something to consider.