Great photos ghostie with the differences. I would also add two more things:
1. M Series: No-tool firing pin bushing that can be removed by hand and sticks out from the back of slide slightly. P7 PSP: Flush firing pin bushing, requires tool for removal.
2. M Series: Extractor is also a loaded chamber indicator and sticks out slightly when loaded. P7 PSP: No LCI.
Also there are two different generations of P7 PSP pistols. The earlier Gen 1s have a smaller narrower mag release, shorter grips and steel trigger. The Gen 2 have a wider mag release, longer grips to make the mag release flush, bobtailed frame and polymer coated trigger to reduce heat transfer.
There is also a Gen 1.5, which is the Gen 1 P7 PSP that been retrofitted by installing the new wider mag release, longer grips, polymer coated trigger and some upgraded internals. This was done at the factory to upgrade German police guns, so a lot of the Police trade-ins P7s come in this configuration. Its easy to spot them as they dont have a cutaway bobtailed frame.
About the P7 PSP vs M8 vs M13. I prefer P7 PSP with flush magazine release for carry, and P7M8 for the range. The M13 frame is wider but it also has slimmer grips so the overall it is only marginally wider at 1.1" vs 1.3" inches. The main problem is the contour and not the width. Its got two semi-sharp corners that dig into your bones with modern thumbs high grip. My hands are large and the M13 can be very uncomfortable after a long range session. The P7M13 designed in a rush to meet the US Army XM9 pistol trial requirements, one of which was high capacity. It seems like it was designed on a CAD computer program by making the frame wider with no consideration for ergonomics. Another indicator of this is the double column magazine that is single feed on top that did not require the redesign of the slide and feed ramp. I am not a fan of the M13 double stack guns as they are a deviation from the original concept of a compact and thin police pistol the original P7 design was.
Anyone that has the same problem with the M13 digging into their hands, try the thumb down hold... it makes it shootable for me, eliminating the pain. Still my range gun is the M8, not an M13 that I have to use a modified hold for.