If 600 grains is enough for supersonic, it ought to be enough for subsonic too:
To add belt to suspenders, center a cannelure on the bullet ogive at ~1.060" from base, or about 0.500" from meplat. Probably not at all necessary.
Lengthening of the .458 B&M throat may be required for some of the above COLs.
Ron aka "Rip" for Riflecrank Internationale Permanente NRA Life Benefactor and Beneficiary .458 Winchester Magnum, Magnanimous in Victory THE WALKING DEAD does so remind me of Democrap voters. Donkeypox.