The CCI standard velocity reliably stay below the sonic barrier, and they are rated at 1070 fps. When I tested them, (50 rds measured) they averaged 1072.3 fps with an extreme spread of 84 fps. The max velocity was 1119 fps. I did not hear any sonic crack from the CCI.
65-year-old Remington Standard Velocity ammunition, in the same test, had a little higher average velocity (1098.9), and a little larger extreme spread, with a max velocity of 1143.
I heard a few sonic cracks with that ammunition.
As the ammunition produced for suppressors is designed to stay below the speed of sound, I expect it will do so.
My assumption is the pistol load is a little hotter than the rifle load to better dance on the edge of subsonic?
It’s so close that temperature can be a factor in going supersonic.
Along with barrel length of course.