I ordered a WOA upper last month, 18" spr barrel. One option that you might be interested in is the Squad Designated Marksman, 20" fluted match barrel available in 1-7 or 1-8.
I plan on shooting up to 75's so went with the 1-7 twist. I don't think it'll handicap me shooting 50 v-max from what folks have said, and the faster the bullet is spinning, the faster it'll come unglued.
I'll probably get another WOA barrel in 20" to build a slightly different upper. This first upper was an attempt at a compromise "tactical" upper that would also offer great accuracy and reasonable weight. The 16" tubes are just too loud, but I figured an 18" mid length wouldn't give up much in the handling department.
