IMR 4064 is a powder I did not experiment much with.
The interesting thing about your results is found in the April 1980 issue of the American Rifleman. They were testing the TC Contender 10 inch barrel in the standard .25-35 WCF.
In the standard .25-35 WCF with 10 inch barrel, 25.2 grains of IMR 4064 behind the 100 grain Speer JSP developed 1,875 fps with 37,000 CUP.
