You are probably going to need a 1:8 twist for something that heavy in this caliber. That will be an awfully long bullet.
"Enter through the narrow gate. For wide is the gate and broad is the road that leads to destruction, and many enter through it.  But small is the gate and narrow the road that leads to life, and only a few find it.
If you find your self in a fair fight, your tactics suck!- Marine 1st Sergeant Jim Ryfinger
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Conventional wisdom breaks down with the really long bullets. Because they are so very long, the lead core and thin jacket make them susceptible to torque. You want to avoid over spinning them. The RPM limit is greatly influenced by the number of lands and grooves.
You can use "advanced search" to go back into the archives about 5 years when they first became available and see how the RUM people fared and what twists they were using. You will also find the velocities they obtained. As I remember it, the 9.5 twist people had some successes and some failures but nobody with a 1-10 succeeded.
This is an area where you really need to do your homework beforehand