I'm shooting them at 2730 in my 6.5x47 with excellent accuracy, I'm liking them better than 140 Hybrids, better in the wind and cheaper. A buddy of mine shoots them also, he's getting 2830 out of a Creed.
I had the same issue, I increased neck tension to .003" and it mostly went away. Still light soot halfway down the neck but nothing near the shoulder anymore. More more neck tension allows the case to expand and start sealing sooner before the bullet is released.
I've been using the RCBS sonic cleaner with the Hornady solution and it get them super clean, primer pockets nice and clean also. One trick though that made a world of difference, I heat up the solution HOT on the stove, not boiling but almost.
H4350 varies quite a bit from lot to lot. Just tapped into a new 8lber and had to go up .6 grains to maintain my velocity. That's the most I've ever seen usually it's only a few tenths up or down.