I should've noted that I'm working on a custom design, not a pre-made board. At the moment things are running off of a breadboard with a couple of 328Ps running with 5V @ 16MHz. Ultimately, the project will be run off of batteries, so while there is nothing wrong with running it at 16MHz, I don't need it to run at that speed. So for battery consumption, I'd like to drop that to 8MHz or maybe even 1MHz - that would still be just fine for what I'm doing ... I think. Definitely 8MHz ... 1MHz remains to be seen.
Using the IDE, I burned the Pro Mini bootloader, and I picked the 5V @ 16MHz since that's the only 5V option from the IDE. But I'd like to change the speed.