I have many 30 cal magnums, including 300 RUM.
There are so many factors in making personal choices. I don't want to second guess your preference.
But
IIWM
If the barrel length of 24" is critical, I would go WSM or WM. Velocity loss of the 300 RUM is greater in the shorter barrel putting performance in the realm of the WSM or WM anyway. Muzzle blast and perceived recoil is greater due to high exit pressure and in burnt powder.
If the barrel length can be 26", I would go 300 RUM and did. Makes your 500 yard parameter with ease.
I have not shot any of my Bartlien barrels (umm well its early, more coffee needed for brain to work well), however, the #3 fluted would be a fine compromise.
I made a 300Wby 26" that is #8.5. Without a brake, not fun for the shooter, with a brake, not fun for bystanders.