I have a .2 GTS(stage 2) and a M3P. When i'm driving the M3 I crave the GTS sound and trans and when I drive the GTS I want that instant torque and all the tech. It'd be hard to choose one over the other. I consider myself lucky and blessed.
I'm kinda in the same boat. I've got my 500hp muscle car with the amazing V8 sountrack, comfy ride, etc. Might just keep it to remind me from time to time what that sounds like. From a daily driver standpoint, I don't think I could ever seriously consider a gasser again. At some point. I'll probably just feel guilty letting the old car mostly sit around in the garage and sell it.