Steve's XP started it's life with me in a rifle form(6.5x308 Imp 30 degree shoulder). I had my 7-08 XP handgun built by Chunk Youngbllod with a planned pistol in the afore mentioned wildcat. After I had the 7-08 for awhile I realized I didn't need something so close to it so I had it made into a rifle instead. I only used it for PD's and coyotes and ended up selling it to Steve. Steve later had it rechambered into the 6.5-284 by Greg Tannel (Chunk is no longer smithing and referred Tannel to each of us). Steve's XP is a combination of Youngblood's/Tannel's work.
My 284 Win XP was built by Youngblood too.
Steve's 6.5-284 has a 1-9 twist Shilen, whereas my 6.5-284 built by Tannel has a Kreiger 1-8 twist.
Tannel is one of the best when it comes to accuracy smithing www.gtrtooling.com Another good one that I have not used yet but will in the future is Kirby Allen (50 or fiftydriver). A third smith I am using right now for a 6-284 XP project is David White. David doesn't have a 6.5-284 reamer yet, while Tannel does (unsure about Kirby).
I am going with a Broughton barrel with my 6-284. Krieger & Shilen have also been very good to me. Tim North of Broughton barrels has been a friend in helping getting the handgun class going in 1k shooting in Iowa. The nudge would go to him for a barrel now in my opinion. Hope this answers your questions.