re: Does anyone here have a Derringer?

Honestly, the best gun for me won't be the best gun for you. My hands are large and a smaller gun is not the correct choice for me. Glock 21 is what I carry, and 2 of them Find a gun shop that has a range and try them out. That will be the ultimate answer to this question.

Power isn't everything. I could carry twin 10mm, in the exact same frame size, but the recoil difference between the .45 is noticeable on shots 2 on. Placement, placement, placement. That is the biggest key in a self defense weapon. Fire what you're more comfortable with.

In my case the 10mm is way more expensive than the .45, but bullet cost shouldn't be a factor in the calibers you're looking at. Practice until you feel proficient, regardless of your firearm choice.

Probably not a direct answer, but it's the best advice I could give you.