[Jeph]

I think we're talking about E46s too much.

However:
CLK AMG - Will age poorly, softer than Porsche
G35 - Too common
350Z - Too cheap-ish, rather have the Infiniti version (see G35)
E46 M3 - Not a fan of the exhaust rasp -best overall of these options, but it's really time for you to step it up.

Just my opinions here.

I would file all of these vehicles as good cars (less for the Mercedes because I don't have much personal experience with them -they're more "class" than "performance" to me).

Let us know how your Porsche test drives go.