if you don't want the .357 Mag... it doesn't do you any good.
Not trying to be recalcitrant but why would you not want a .357?
I grew tired of the muzzle blast, violent recoil, and ear-shattering report of the .357 Mag. (Yes, I use hearing protection; but I also hunted with it.) I still own one K frame S&W in .357, but it is only used for .38 Special plinking.
If I have a legitimate use in mind (Hunting, target practice, Home Defense, personal defense), I always find myself reaching for something else. From bottom to top, it could be anything from .380 ACP, to 9mm, to 10mm, to .44 Special/Mag, to .45 ACP.
The .357 Mag cartridge is a wonderful thing. I will not deny that. However, I want to give the .327 a try. Muzzle blast and an ear-shattering report may come with the package, but it's something else to throw in the line-up or leave on the nightstand. It will also give me .40 S&W/10mm power in a revolver, without using (half)moon clips.
The .357 serves different purposes in my arsenal.
Which is?
At one time, I had 4 S&Ws chambered in .357 Mag. I used to hunt with them. I used to carry them as SD guns while hiking. I used to do a lot of things with them. Now, the only survivor is basically a paper weight that stretches its legs to plink a few times a year; if it's lucky.
And, back to your first question:
Not trying to be recalcitrant but why would you not want a .357?
Why would you not want a .416 Rigby? Why would you not want a .257 Roberts or a 7mm-08? Why would you not want a .25-20? Who, in their right mind, would not want a .30-06?
It is all a matter of personal preference, experience, and application.
I own several .22 LRs, a .22 WMR, a .22 Hornet, a .223 Rem, a .220 Swift, a .243 Win., and a .270 Win. just for my 'small' caliber rifle line up. They can be stretched, or loaded down to cover
anything I hunt or shoot; with varmints being covered pretty heavilly by the mid-range of that spread. I won't even get started on how each rifle also has its own combination of stock, scope, trigger, barrel dimenions, rifling, chamber tolerances, and weight, which also contribute to how the rifles are used. Many people ask why I own XX caliber when I already have XX. It's not just a cartridge. The design of the rifles themselves contributes immensely to how that cartridge performs. It's the total package.
When I look at a cartridge or firearm, I'm not just looking blindly at a ballistics chart, or the design of the weapon itself. I'm looking at how everything will work together.
For me, it's the total package. The SP101 .327 Federal is a package I want. And, I probably wouldn't mind trying it in a 7.5" Redhawk, either.