I'm not certain about the differences between the Spyder and the GTS 4.0 when it comes to the shifter, but I assume that they aren't significant. In any case, in my opinion, there is a very substantial difference between the M2C and the Spyder gear shift feel and the clutch take up and feel. The Spyder is way ahead, and you'll certainly enjoy the upgrade. I'd agree with the many reviewers who have said the 982 GT4/Spyder have the best manual gearshift and clutch setup out there.

The exhaust question is a big topic, and you'll find many threads on it if interested. I'd suggest you read through them if you want to consider a change from the OEM system. My complaint, and that of many others, is that the sound quality was a big let down when compared with the 981 PSE system. The high pitched scream was gone, and the tone was not nearly as clear/distinct as was the 981. Also, the OEM valve operation is intrusive on the 982. I am very happy with my Akra link pipe and slip on system, particularly because it does not drone while giving me the kind of sound I expected. It was a huge improvement in my view. I did not replace the headers with the stock cats, and so I really don't expect any warranty issues. However, there are likely some different opinions on this. In any case, the OEM link pipes don't provide any emissions functionality in the US, and I've never experienced or heard about engine warranty issues related to cat back exhaust upgrades, so I'm not concerned.