A 1-12 twist is plenty fast enough to stabilize any bullets you might shoot out of a Savage .30 caliber rifle. I don't know where you heard the differing malarkey. If the gun shoots 180's better than 150's and you like the 180's, then by all means use them.
Calhoun is right as rain - it's all about bullet length not weight when it comes to stabilization in a given twist.
As for shooting thin jacketed .30-30 bullets at .300 velocity, you'll experience tremendous expansion for sure.
Short necks on .300 brass aren't much of an issue, and then mainly in the area of concentricity. It's easier to attain straightness in a loaded cartridge with a long neck than a short one. Beyond that don't sweat it.
Frankly, if I were hunting where a swipe at an elk was a possibility I would probably load Barnes TSX's of 130 or 150 weight. Note they are monolithic bullets and will equal the length of heavier cup-and-core bullets, but offer the advantages of higher velocity coupled with excellent expansion and penetration. And they'll certainly stabilize in the twist of your rifle.
