I finished my speaker swap project on my M3P over the weekend. Here's everything I swapped:
Sub: Skar SDR-8 D4
Front dash speakers: FaitalPro 4FE35 in the corners, 4FE32 in the center
Front door woofers: Dayton Audio SIG180 6.5" with RWAudio adapters
Front door tweeters: Dayton Audio AN25
Rear door speakers: FaitalPro 4FE32
What's still stock/what I'm not changing: Rear deck speakers, headliner speakers
I haven't had hours of listening time yet, but initial impressions of the current system are very strong. I'm not quite an audiophile, but merely an enthusiast and thought the OEM system was very good out of the box, but there's certainly room for improvement. My non professional thoughts are that the new system is fuller, richer, clearer and punchier. The Skar provides much more low end extension. The only other thing I might like to do is add a dedicated amp for the sub.
I was going to retrofit a center dash tweeter, however my dash has that hole completely filled in with plastic and I couldn't figure out a good way to cut it out with very little working area. I may still decide to go back in and figure something out, but we'll see.