There are a couple ways to look at it. A 700 that been trued properly will have an action face and lug seat square to the bolt bore as well as concentric threads. The bolt lugs and face are also square to the bolt body. The main accuracy gain here is even lug contact. You can see the accuracy gain after fixing lug contact even in a hunting rifle. What you will still have is a the stock ignition which is the other part of an action that has a big effect on accuracy. You can have the shroud worked on and firing pin bushed to get the ignition up to par. You can also time a 700 to be every bit as smooth as the best customs. You will want a good recoil lug double pinned to the action so when you get a new barrel the lug will be in exactly the same spot and not cause a bind in the bedding. I also like to use 8-40 screws and double pin the rail on the magnums. It all adds up. The flip side is that most customs are not that good out of the box anyhow. So many smiths put work into them as well. In some cases your better off starting with a 700. However the one I usually recommend to guys thinking of doing the 700 is the defiance tenacity. They stand alone in that price range imo. The ignition design is good and they are straight.