Yeah, the turning circle increase is noticeable, but its not a huge difference and the XVI will still out turn most of the other late war fighters easily, and the roll rate increase is useful because the Spit IX's roll rate is quite poor compared to fast rolling planes like the Fw190 and Yak-3. My personal preference is for the standard wings, but its more because I like the way they look than because of any real advantage
I'm not sure if
all the info is valid in game, because I don't know if the MkXVI has the cockpit it should have or whether it as the MkIX's cockpit, like the Yak-3 has the Yak-1's cockpit, which would mean you wouldn't get the improved visibility you should be getting from the bubble canopy, but apart from that the rest should be valid, because the flight models are very detailed and authentic.