Can't help with your "exact" load, but with 53gr. Sierra Flatbase I show that I have loaded them at 36.3gr. of IMR4064 with a speed of 3669fps. My notes show a .621" group with that load.
If you can find some 4007SSC give it a try, only problem is Hodgdon/IMR have discontinued it, but there is still some floating around.
Hope this helps.
P.S. See your from Fallbrook, spent quite abit of time there back in the 80s, when I was in the USMC.