Have you tried RL-33? Rcamuglia is a real RL-33 fan and shoots some impressive speeds/groups with his .264 WM.
The Nos with US869 can reach 3,300 with 140's, but burns more powder than the .264.
.264 WM fans seem to like the round. My experience with it wasn't so good; I found it to be fickle.
The 26 Nos has been more straight forward, at lesat for me. The secret is ultra slow powder, US869 being the champ. Pull down WC872 is about a US869 clone, at least in my experience. And, 872 is cheaper than 869.
DF
