I own a full custom 338, and I have shot my buddy's TRG-42 quite a bit. The TRG is a very nice rifle. Great trigger, smooth and solid action, good ergos. That rifle shoots 0.5 MOA with handloads. I think you would be quite happy with the Sako. Just make sure you get a newer one with the 10 twist barrel. The older ones had 12 twist.
Should you decide to go custom, I will relay the same bit of advice my gunsmith gave me when I set off on my 338 project: consider the 338 Norma. The Norma is much better suited for slinging 300 grain (or Flatline) bullets from a magazine, and will give almost identical ballistics to the Lapua. I am running an improved 338 Norma; no sweat to push 300 Bergers at an honest 2900 with RL33. And that short/fat Norma case gives some pretty incredible accuracy. Just some food for thought. I totally understand the Lapua itch, and I will eventually build an improved Lapua on a single shot action. But for a repeater, the Norma deserves serious consideration.