RL-17 at 40.4 gns around -2700 fps 24" barrel 140 gn bullets. Superformance at 44 gns, around -2700 fps 24"barrel 140 gn bullets. These are my alternates to H4350. I searched these out because when I started reloading a year ago, I could not get H4350. Now, I don't need to, though I have some. And get the same performance using 41 gns of it. (note all these charges are under max, which was a self-imposed spec of mine) From what I have read, Hornady developed the 6.5 CM and they originally used H4350 as the powder in their Amax 140 gn cartridges. IOWs, H4350 was the original powder used. I'm guessing that is the reason it became so popular in our crowd .
I'm using an RPR and these loads group at 1/2" and I've ran them out successfully hitting 8" & 12" steel plates to 800 yds. My rifle 'likes' 140-142 gn bullets and MVs +/- 2700 fps. They shoot as well or better than any of the factory box ammo I've tried (which has been most of them. Hornady, Fed, Win, Nos.
And thanx to the other contributors to this thread as I've got a couple new powder ideas now. In fact, I can thank forum members here and on Accurate Shooter and 6.5 CM and Youtube (Johnny Reloading Bench, Ultimate Reloader, Bolt Action Reloading) for giving me the ideas for the powders I am using (above) and starting points (charge weights). I've got 12 loads I have high confidence in. Fired a total of 313 rds, counting cold bore shots. I did this by doing pretty much the same as you are doing. Get on line and search around and ask around. I'm sure, my doing that, is the reason my round count developing these loads is what it is. Good luck to you!
PS: these loads work in my RRAs (AR) though slower MVs due to its 20 " bbl. Mag dimensions limit me to 2.80 & 2.81, so my COALs here and above have been to that length.