A larger prop with less pitch WILL have a breaking action so to speak, But, as you said yourself, a plane can't fly below it's stall speed. That's where other factors come in to play. Moving the CG back will decrease the stall speed, but there's a limit there too. The next thing would be to add flaps and/or slats. I have a 40 sized Ultra Sport that I added flaps to (in case you're not familiar with the US40, it is a very fast plane) when I drop the flaps, it is almost comical how slow I can get it to fly. It will fly slower than my Piper Cub!