First, you're off on the barrel length. The 57 never came in 6.5 inch, just 6.0 inches and four inches. And I think in 8 & 3/8th's inches, for those who like long barrels...
I would DEFINITELY select the six-inch M-57. It'd handle the blast and recoil better and give added velocity and is just a nicer gun. The M-58 was just a bigger M&P service gun.
Also, I once fired another shooter's M-58 with fake pearl Magna stocks. It was absolutely the nastiest kicking revolver I've ever shot!
Frankly, unless there's some reason why you want .41, buy a .44 Magnum. Ammo has a wider selection and is much more easily found.
As for glamour factor, we all know Dirty Harry's .44 and it's been in other books and movies. The only place I've seen a .41 Magnum mentioned outside of gun literature is that Modesty Blaise used a .41 on several occasions in Peter O'Donnell's novels. And one bad guy had one. The author didn't mention model, but I'm pretty sure he knew only about Model 57.
Any man or animal you shoot with a .41 will never know if it was a .41 or .44 Magnum. If anything, I lean a little toward the heavier, longer .44 bullets.