I've got both a 9P and a M3. If I had to do it again and only get one: I'd probably get both
For an around the house / nightstand / bag flashlight: I reach past the 9P for the M3 every time. HAIII, Shock isolated bezel, mine's got the strike bezel.....
To go in the back pocket of my pants when I go out and expect to want 200 lumens: 9P because its thinner (see below for more info though).
I originally added an A19 to the 6P but I bought a 9P because I didn't like the extra point that needed to be screwed. I found that everytime I picked up the light i'd re-tighten the A19 / 6P connection just out of habit and not being sure etc. I wanted to keep it simple and i felt the 9P setup was more durable because it was only a one piece body...
To let you know, I hardly take the 9P in my back pants: I usually have my L4 in a pocket and my G2Z or M3 in a bag...
If I were in a position to choose one or the other: I'd save more and get the M3. But then this 9P deal might be a real bargain.
I just noticed you already have a C2 with P61. The output of the M3 will be substantially more, but as Unicorn has said, you might need to look into a turbohead to see an improvement in throw. As far as 'punch difference' with lights: to my eye the M3 and 9P are comparable. If thats your main goal, then maybe trying an A19 and a P91 wouldn't be a bad idea before you drop some bigger money...