The PF9 is like a large P3AT.
The PF9 is not much different in size from the P11. It is just a tad lighter, and just a tad thinner, but about the same dimensions. If you have a P11, but don't have a PF9, you really aren't missing much. But, the PF9 does have the lighter, smoother trigger of the P3AT.
Here's a comparison photo of the three guns:

Click image to enlarge