I was considering moving to an F10 M5 soon from my E90, but after driving 550 m sport and the new M6 vert I changed my mind right away. They are just way too big and don't feel anywhere near as sporty and involving.
I agree the panamera is nice (I spent 2 weeks driving through Germany/Switzerland in a S). The interior is very nice, but it is very expensive for the relatively low level of performance you get with the S and going to the turbo or even GTS is a big price jump. Although it was nice at first I quickly got bored with the PDK and was wishing for a manual. The panamera drove smaller than the F10, but still certainly didn't feel small.
Right now the front runner for me is a 991 S. It is a significantly different car from the 997. It has an excellent interior with all the features you'd ever want, feels much more roomy and comfortable than the 997 while being lighter, still has amazing performance with an NA engine and manual trans, sounds great and gets much better mpg. Not wanting to go turbo or auto trans or bigger car there really isn't much else out there that I would give up the E90 for.