Tough decision. I would probably get the new Cayenne GTS and keep the M3. Upgrading from a used M3 to a new Carrera S has to be a much bigger gap than the used Touareg to used Cayenne gap. That's why I suggest the new Cayenne. The new Cayennes are a quantum step up from the old ones.
-2016 Macan Turbo(GF vehicle)
-2017 Ford Raptor