Rate of twist

[Cossack]

You're good for nearly any load. It's hard to over stabilize a bullet. A very light frangible bullet may blow up if pushed too hard esp from a fast twist barrel but that would take more that 1 in 9.5 TR.
BTW, if you handload try the 85 gr Barnes TSX. These solid copper bullets get nearly 100% wight retention. They will give you penetration and expansion like nothing else I'm aware of. Since they are relatively light the velocity will be up too.
Make your 243 shoot like it's on steroids.