Those are nice barrels for sure and I think for a dedicated 3-gun upper, the stainless makes the most sense. The only thing I'd mention about the barrel is that I prefer a lighter contour than 38 oz. like the 32 oz lightweight Noveske. But it's up to you if the added cost is worth it.
If you want to go the whole Low Mass route, you're going to want the adjustable gas block, Low mass bolt and buffer. All JP makes the most sense although I mixed and matched.
Hope that helps.