Well the 300WSM (338WSM Parent) holds abit less powder than the 338 Winchester mag and I now that the old 338 winchester can get the 250's up to 2700+fps with a 26" barrel and the 300WSM can get the 220gr bullets up to 2700fps with a 26" barrel.
I'd say that with the 27" barrel and the 5R rifleing that you should be able to get to 2650fps or damn close to it , you may even get a bit over it.
the 338 WSM is a bit more powder effecient than both the 338 win mag and the 300 WSM
, and the 5R rifle egneraly does help with increased velocity.
As for brass , Winchester is good stuff if you go throught he trouble of sorting and case work , the Norma is the best for accuracy sake but its coslty and soft so if your running high pressures it won't last.
I had to make a set of dies , I'm not sure how big Redding goes up with their neck bushing but if they go big enough you could use their 300WSM dies with a bigger bushing.