[attila]

First, I do not want to provoke any fierce response with this thread from the e92M3 vs M4 "debate group". It is more intended to be a sort of observation on certain aspect of these cars not a real comparison.
I just got my 991 GTS4 (manual) and drove relatively extensively a new M4 (DCT) and brought out my 997.2 GT3RS from hibernation.
I have to say I almost never like my new cars right away, just search my old GT3RS thread, where I said some not so nice things about that car and got lots of heat from the Porsche lovers.
It was a tough decision between the M4 and the GTS4 for me. Obviously I could not test drive the GTS but did test drive the 991 C2S a few times. My impression was that that the two cars are basically equally quick but the M4 felt quicker due to the torque low down.
I highly doubt that the GTS4 is quicker than the M4 even with the extra 30BHP over the C2S. It is faster than the e92M3, as expected, but not by much. In everyday life situation the difference is negligible. Of course the GTS4 being AWD can put down the power much easier so off the line is noticeably faster and you can go full throttle without the EST kicking in. The GTS4 sound very nice and sophisticated, specially the flaps open (sport exhaust) however, my e92 sounded equally nice, just different. I miss the V8, well the S65 I mean. In comparison the 997.2 GT3RS sounds completely mad, savage and illegally loud (with the RSS bypass). Rather not to discuss the sound of the M4 here.
I loved my M3 seats - I know some didn't - the Porsche seats (18 way sportseats) are similarly good, maybe a tad better. The single biggest improvement is the transmission. Had my reservation about this new 7 speed PDK derived unit before I actually drove it. Now I love it in the GTS. Some say it is slightly reworked in the GTS compared to reg. C2S. I only tested the MDCT m4 so cannot comment on the new manual. By the way the RS manual is more of an exercise program than a shifter. You have the feeling it would survive a direct nuclear hit, maybe it would became smoother in the process, I don't know. It is fine on the track, annoying in traffic. In general the GTS is way closer to the new or old M3 than to the RS. The RS is still more of an occasion and requires way more attention than any other street legal car I drove.
The GTS rides a little better than my M3 did in comfort setting. (my reg driving) very controlled due to the PDCC, no lean, etc. I think this holds true against the M4 as well.
Could not finish, will continue!