N560 will give the same if not better velocities than R26 with less pressure and is not temp sensitive . R23 is a good burn rate for the 6.5 PRC, if you are using mag primers , go too standard primers and you will be able too move up in the powder charge with a vel increase . I used too use mag primers in my 6.5 PRC , but Steve from Hammer bullets recommended trying the standard primers for max vel and it worked it allowed me too move up in my powder charge , getting a more efficient burn down the barrel.I liked RE26 because it provided excellent accuracy in several cartridges. The higher velocities were a bonus. At the time, I had no problem finding an 8lb jug. Most of my loads were worked up in the spring when temperatures were in the 60s. While the stories of spiking pressures with RE26 became commonplace, I continued to shoot in the 70s so never experienced any issues myself.
While I was on the continual hunt for H1000, I was able to find an 8lb jug of RE23. As my supply of RE26 was diminishing, I started to work with the RE23. I was pleasantly surprised to find that accurate loads were easy to find and that attainable velocities were still good, even though they were not as high as the RE26 loads.
I was running the 124H bullets at 3,300 ft/sec with RE26 from my 23.5" Proof barrel. The RE23 loads shoot just under 3,200 ft/sec. That seemed like a good trade for a temperature stable powder that I had on the shelf. Both loads shoot sub .5 moa at 417yds.
The interesting thing about RE26 is that some reloaders seem to experience temperature related spikes while others have not. Some have apparently seen spikes when temps are in the high 80s while others shoot in the 90s without issues. I'm content with avoiding the issue all together and since RE26 is only available at the end of a rainbow, it's just not in my reloading equation anymore.