With both the 127 TTSX and 129 Nosler ABLR, 60.5 grains of Retumbo has worked really well. In a 24" barrel velocity is a little over 3000 fps. In my custom rifle, both bullets shoot best seated around .1 deeper than the SAAMI 2.95" OAL.
The best load with Hodgdon/IMR powders for bullets in the 140-grain range is the max listed charge of IMR8133, for 2900+ fps.
Haven't tried RL-26 yet, but plan to, probably after some pressure-tested data appears. My experience with 26, in several rounds, is that it doesn't show "pressure signs" until well above 65,000 PSI. Nothing wrong with that, but whether it's "safe" is another question.
You might check out the 2019 Hodgdon Annual Manual for more detailed info. Somebody wrote an article for it about loading the 6.5 PRC.
