here's a 3 shot group pic of my 2nd time shooting my 300 WBY McWhorter Rifle-
although it looks off center it's not, it's just how I set the target on the washing machine to take the pic and my wife had clothes all over so I had to turn it--
anyway I will say that I never expected to buy a custom rifle as I continually tinker with my guns also, but I just got a burr up my butt to have one and I bought it---wow am I impressed and highly recommend McWhorter Rifles to anyone who wants to drop the coin---they were great to deal with and they did a great job getting this gun to me in time for my Montana hunt(unfotunately I didn't pull the trigger)
so I would say yes they are worth it, even if you tune your existing gun it will help---chris