Photobear,
Although I agree with other posters about the ammo availability issues, your original questions were about power & recoil, especially related to .38+P and .357 loads.
Let me assure you, when you pull the trigger on an SP-101 in .327 Mag, you will know that you have unleashed a magnum round! You feel the torque, see the flash, and hear the wicked blast of a magnum. Ignoring ballistic tables for a moment & basing my comments on purely subjective firer's impressions, I'd say that I agree with the assertion that the .327 is between .38+P and .357 Mag in power levels. Felt recoil is less than a .357, and my perception is that flash and blast are also similar, but somewhat less than .357.
Personally, I would feel confident using any of the three for SD, although they generate effectiveness in different ways: caliber, expansion, permanent cavity, temp cavity, etc. Again, questions of ammo availability aside, your decision is whether you personally feel OK with a small caliber--high velocity solution to SD/HD or not. If you're OK with that, the .327 is a peach.
Final note: if the school of thought is correct that most "stops" with pistol ammo are psychological in nature rather than physical, then that could account for some of the .357's legendary effectiveness. . .kind of a projectile-firing flash-bang when you touch her off, and the BG definitely will be aware he's being shot at! The .327 Mag shares these qualities in great degree. If you shoot one, you will not be disappointed in its power level. (But I hope you're into reloading if you choose .327 over .38/.357.)