The M1 carbine has been chambered for cartridges that are simply insane. I remember one that was a .50 caliber. There was one that was a shortened .308, called the .30 Kurtz. A similar cartridge was made by necking up to .357".
Now, the big kickers tend to break stocks, bolt lugs, and who knows what else. That is not the gun's fault, though.
Like others, I would be reluctant to rechamber a GI, and reluctant to risk money on a clone. The 5.7 mm Spitfire looks like a cute package, though. There was on on a shelf at a gun store for several months that tempted me.
In the end, the JHP .30 carbine is pretty effective. If I were going to consider my Saginaw Steering for serious purposes, I would use that load.
Remember, when Maj. George C. Nonte and others were converting these carbines, they were widely available and relatively cheap. No wonder people use the AR15 platform for so many conversions today.