Alex,
I'm going to give my good experience, bad experience with Shilen.
I had them put a 28" barrel and brake on my 416 wby. It shoots absolutly awsome!
I then had them put a 28" barrel and brake on my 338-378 wby. After several frustrating months of inconsistancy.......the rifle would shoot bug holes one session then 1 1/2" groups the next, or group high or low from a previous session. After several scope, ring and bases changes and remounts I sent the rifle to Kirby Allen (fiftydriver) to evaluate. After dissasembly, he informed me that Shilen had screwed up the threads and had compensated by using locktite to secure the barrel in place.
Kirby installed a new Lilja tube and now all is well.....all bug holes all the time /ubbthreads/images/graemlins/cool.gif
In my opinion you should look to the gunsmiths on this site who are very capable of building precision rifles for magnum high intensity calibers. Kirby Allen or Shawn Carlock can both build you a rifle that will be awsome, and probably will not cost anymore than Shilen.
Just my opinion and sugestion for what it is worth.