I have heard a few 197s getting 18-20!!!
I got abused when I said that, at least I know I didn't dream it now heh!
Back on topic though - great cars. Feel so very sure footed, but not in a boring way, the chassis still feels alive. The brakes are pretty much the best certainly I've ever experienced on a road car, and I've driven the odd fairly high end motor (shame none of them were mine heh!). Way better than even the 4 pots on the Vee imho. I'd be controversial and choose not to have the Recaros, mainly because I found them a bit hard - and I have a bad back heh. Also, a few too many reports of them wearing badly for my liking...
You probably wouldn't have any more fun than you can in your Cup, but you'll also probably be quicker point to point or on trackdays if that's your thing. Also, as others have said, the interior is in a different league.
Really you'd have to weigh it up, drive one, see if you fall in love with it
Dan