I cannot say for sure, so I will state my opinion expecting someone with more knowledge than myself to correct me if I am wrong, but I think you should be able to stabilize something a little longer than the 55s in a 12 twist. I shoot the 55s in my 14 twist with no problems....well no problems until past 700 yards. They often hit my 800 yard target sideways, but so do the 55s shot out of my buddies 12 twist. (I cant say for sure but I am pretty sure it is dependant on humidity, some days nothing but round holes) I found one of my 55 bergers that shot completely through an amadillo at 800 that wedged itself in a vine. The only deformation to the bullet was where the rifling engraved it.
I admit that I know just enough to be dangerous.....but dangerous at ever extending distances.