[jphughan]

I would say that the main things to consider upfront are how you value NA vs FI engines based on how you plan to use the car (or of course what your preferences are even if the opposite might be "better" for the majority of your use) and how much you value chassis dynamics compared to torque and power, since there's fun to be had from each attribute but most people if pushed will always prioritize one over the other. The Cayman is going to have the advantage in being mid-engine and significantly lighter. The 3500 lb figure for the M2 is the major letdown in what otherwise looks to be a great offering IMHO, especially given that the M4 gives you a lot more car all around for very little additional weight penalty, albeit with a larger than expected price differential given how much on the M2 is standard. I still personally think the M2 at its size should have been 3300 lbs tops, but it is what it is. I'm however biased because I had an E92 M3 until recently but after I drove a friend's BRZ, I was awakened to the virtues of a lightweight car, and I vowed that I would never buy a fun/track car heavier than my E92.

On the other hand, the M2 has rear seats as you note, and I've seen several forum members say that the joy of taking their kids with them for a drive far outweighs any performance superiority of some other 2-seater car, so weigh that one carefully. And if those considerations don't sway you firmly one way or the other, you can of course go test drive a Cayman S now to see what it would be like, but since Porsche's option list is the exact opposite of the M2's option list, you might want to find an ordering guide to see what's important to you to aid your shopping, and even your test drive. For example, the Cayman S has three different suspensions: standard, PASM (2-mode active suspension), and X73 static "sport suspension", each one 10mm lower than the last one. X73 is considered the best handling overall, and PASM is considered the most versatile given its comfortable Normal mode and still very capable Sport mode. X73 cars are hard to come by, though.

The nearest direct experience I have with the comparison you're looking for is a test drive in a Boxster S with X73 suspension and time spent on back roads in a friend's 1M, but the time in the Boxster was fairly limited and not on fun roads, unfortunately, and my GT4 experience probably isn't a fair comparison. One thing I distinctly remember about the Boxster test drive though is that you have to hold gears longer than you'll be used to based on modern BMW experience, and this was true even though my tester had PDK. The 981 platform has fairly long gearing (6MT even more so), which made me short shift, and the lower power of the Boxster compared to my M3 meant that the short shifting left me with much less power than expected, so that will take some getting used to if you go that route, whereas the M2 I'm sure will have plenty of thrust even at higher gears and lower RPMs thanks to its gearing and being FI.