Will,
I know a certain person that would have a heart attack if he saw groups in the 2" range at near 2600 fps. in a 10 twist 30 cal. bbl.
I understand you want to take it as far as you can with better accuracy(so do i), but take a little time to pat yourself on the back for accomplishing whatn you have done so far.
One thing that stands out to me is that with both the xcb and the 165a bullet, is that after you passed 24 to mid 2500 fps., groups opened up with the 4350 UNTILL YOU HIT ABOUT 47 GR. ......In both cases groups started to shrink again.
As to what to do next? My opinion would be concentrate a bit in that load range with both bullets with full length and neck sized, and try leaving the flare on and taking the flare off the case...all with the same loads.
It would only take a few groups to check all that. Maybe load a few in 2/10 gr. increments past 47.
I did what your doing summer before last, and quit right at the spot you are now.
As i was hitting 2600 fps., groups were coming back in, but lol, hunting season was coming on.
I took my best load at 2450 fps., went hunting, and killed my deer that year with it.
I mean to get back to work with mine too this spring and summer.
HHHMMMM, i also noticed your getting a bit more speed from the 165a in the same load ranges.
Looks like another 30 cal. bullet i need to try out.