I am leaning towards the G26, but am concerned that the 9mm and short barrel = less stopping power, so the G27 might be a better choice.
Where can I find ballistics comparing the G26 & G27 vs. normal barrel lengths?
Every gun is different. Some have much faster barrels than others, so you will frequently see shorter barreled guns actually out-doing longer barreled ones, the difference between the 26/27 and the next size up is only a half inch. Different lots of ammo will be slightly different as well. The 30 feet per second thing is a pretty good general estimate.
Energy numbers are useless, these are service-caliber pistols, not varmint rifles. A well designed bullet will easily outperform a poorly designed bullet loaded hotter. The difference between 9mm and .40 is basically invisible with current loads, it's nothing like the difference between 5.56 and .308. When the .40 was introduced, handgun bullet design was basically still in the toddler phase of its life. All we really knew was that light and fast bullets expanded ok when you made a hole in their nose, but didn't penetrate well at all, and heavyweight bullets could be unreliable expanders if they just had a hole stuck in their nose.
.40 worked particularly well because it has enough mass and momentum to penetrate well almost regardless of how fragile the bullet is, unless you load it with 135s, and it had enough space to put a pretty large cavity in the nose, which combined with it's fairly high standard velocities allowed it to work pretty well even with the older generic JHP designs even in heavyweight configurations.
It also was developed right in the middle of a major period of improvement for JHP designs, so there weren't a whole lot of truly old-tech JHPs ever introduced in .40.
There has been a ton of improvements to handgun bullet design in the last twenty-odd years, the JHPs of today don't need to be driven as fast as possible to be super reliable and consistent performers, lightweight bullets offer almost no benefits compared to heavyweights now, and velocity and energy are pretty much meaningless as long as you aren't shooting something that's been loaded well below the caliber's potential.
"Power" of a cartridge doesn't really have any bearing on terminal effectiveness when you're talking about handgun bullets, and it's pretty flexible anyway. Bullet design directly influences effectiveness. Energy is even more meaningless.