Taz,
If you are making a custom rifle you don't need a barreled action - just the action. You will probably be selecting a barrel from one of the after-market makers so why pay for the barrel? I looked for a while to find the Rem. 700 action that I built my .358 Win from and got it used and had the smith go through the process of truing it all up so that I could learn what was needed so that the next time I could try it myself. Either action will work and both will be hard to find or expensive. If your budget will allow it and your project will benefit from it, there are custom actions that are even better
than the Remington 700 in some instances.The best advice that I can give is to spend a little time asking your smith questions and a lot of time listening to what he says.
PaulS