Stick with Retumbo. Alternatively, consider trying H1000. Like you, I have a 32" 300RUM and have tried H50BMG and while accuracy was outstanding, velocities were very low (~2750 as I recall).
Also, your barrel is brand new. As you shoot it, you will find that it will speed up. My rifle started out shooting the 208Amax at 3150. Without changing anything about my load it has steady crept up to 3275.
You can read about my rifle here:
My 300RUM by MCR
Show us some pics of your shootin' stick!