Concerning noise CRT-GTS : I asked the question to an old german man who ownes both (
) at the M festival this year : exactly the same.
Concerning noise CSL-GTS : Sure you have a better and louder sound from the engine itself due to the enormous carbon air box with the older sister. But from the exhaust, IMO, the GTS is ten times more impressive and "powerful"
And you can go one step further : I met a german guy who owns 1M, CSL (Lightweigt's demo cars), GTS,... and also owns "Titanauspuffanlage.de"
He has a home-made exhaust on his GTS, you just can't imagine.
He also owns now an E63 M6 with home-made exhaust : V10 fuck them all... !
"I can make it even louder but enough problems with police like that"
Finally, I took a ride of the Ring with the GTS this september. The one you see on those pictures but which is now set for the ring : 2cm lower, KW Clubsport kit completely set + a geometry : This was absolutely astonishing !
8:25min BTG... for my first session ever on the Ring. I do not even always know which side is the next corner and I was on Michelin Pilot Super Sport (not Cup semi-sclicks !). Finally, I'm a 20 years old boy with a good idea of what driving is but absolutely no experience on a track !
I asked this german guy for a CSL form Germany and his answer was : "keep your 1M and optimize it, you fill kill this old CSL !"
But today no 1M or CSL : GTS for the track and I have a standard E92 DKG M3 for daily use, once more the V8 is the V8...
In conclusion I would say that you must drive those cars to choose one, every are so different. You can own every ///M model, you will not have two times the same car.
They all share about the same incredible balance, but all the rest is specific to every ///M... and I love them all !