In comparing the most effective options side by side, I find that the KPS system is the most comprehensive.
Here is how it works:
Multiply the Muzzle Energy by the Cross Sectional Area and the Sectional Density of the particular bullet.
Muzzle Energy calculation requires the use of the Bullet Weight and the Velocity of the bullet,
Cross Sectional Area requires the dimensions of the bullet
Sectional Density considers the penetration capability of a particular weight and diameter of the bullet.
So, by using the KPS system, you are taking into account (empirically) the most important features of a bullet's capability to do its job effectively.
The only thing that the KPS score cannot consider would be bullet construction and the difference between one style of bullet (hard cast vs HP for example) in the terminal performance of a particular bullet choice.
Using this system, I have learned some interesting things:
Based on advertised velocities (because I don't own one) a pistol like the Charter Arms Bulldog in a 44 Special, pushing a 200 Grain Bullet at only 900fps is going to have less "Umph" than a Glock 27 shooting 200 grain 40S&W hard cast ammo from DoubleTap at 1009 feet per second... even though the 44 Special will likely have more recoil, and fewer round capacity. Even the 357 Sig out of a Glock 32 will have a slight edge with a 125 gr bullet at 1480 fps (an 8.53 KPS score vs the 8.07 score from the Bulldog).
Here is something else VERY interesting IMO:
Most reported velocities for the G29 (10mm) out of the relatively short barrel that I found showed 180gr bullets at between 1200 and 1240 fps. That gives a KPS of around 12.
However, a Glock 27 (40S&W) with an aftermarket KKM 4.5 inch barrel, shooting 200gr DoubleTap ammo is clocking 1106 fps, for a KPS score of 12.19. In this case, the Glock 29 weighs nearly 7 ounces more than the glock 27 when loaded and with comparable options.
Adding in a 6 inch barrel to the G27, and you get 1150-1175 fps for the same 200gr bullet, and a 13.18-13.75 KPS score. By comparison, the Buffalo Bore 220gr Hardcast out of the short G29 10mm barrel is only doing 1050fps, and getting about the same 13.3 score on the KPS scale. Even at the upper limits of the G29's 3.5 inch barrel with DoubleTap's 200gr HC at 1240fps, the KPS score is only 15.33, which is only a marginal increase in firepower over the G27 at 13.75 KPS, considering the weight penalty.
On the other hand, putting a 5 or 6 inch 10mm barrel in a G30S (with the lightweight G36 slide) the weight penalty over the G27 is only about 2-3 ounces, but the DoubleTap ammo is pushing a 230gr Hard Cast bullet at more than 1120fps (4.5 inch G20 barrel length) which gives a 16.54 KPS, or the BB 220 HC at 1200fps gives a KPS of 17.37. That is where we start seeing the 10MM get close to 41 mag capabilities (which put the 41 Mag at about a 19 on the KPS scale).
It is also interesting to see where venerable cartridges like the 357 Mag come out in all of this. Out of a 5 or 6 inch barrel, it can get up to the 15-16 KPS range, but out of the short stubby barrel lengths, it is clear down about 5-6KPS... which is LESS than Buffalo Bore 9mm out of a Glock 26.
In fact, just the difference between the Ruger LCRX 38 Special with the 3 inch barrel vs the S&W 340PD 357 Mag with 1.8 inch barrel puts gives the 38 Special far more velocity (grain for grain) than the 357 mag, and a 7.2 on the KPS. So, by my research, for the 38 special to beat (ballistically) the 9mm, it needs to be fired out of a 3 inch or longer barrel.
If recoil wasnt an issue, this would put pistols like the S&W 337Ti 3 inch 38 Special Kit Gun (only 12 ounces with a 3 inch barrel) at the top of the list for utility and weight compromise. It would be lighter than any compact 9mm, and have more energy and velocity than its 9mm brothers. Likewise, the S&W 386 Mountain Lite 357 mag with 3.25 inch barrel and 7round Cylinder would also be an excellent option, at only 18.5 ounces, it would weigh an ounce less than the G27 (with the same number of bullets, but have the capability of getting the 357mag bullet to velocities in the 13-15KPS range. However I would guess recoil would be ridiculous with full power loads out of either of these options.
Thoughts?