Personally I would say read out the reviews on the rx8's that should be enough to convince you the 350z is the way to go.
Rx8's in general are cheap for a reason, many have or end up with hot / cold starting issues. Don't like being started and shut off without fully warming up (a 3 hour+ wait or a try at the de flood process) rebuild wise that's £1500+
The rotary lump is nice and revvy but not practical, more of a second car toy that you don't mind if it goes pop or gives up. Nice looking don't get me wrong just hard to live with.
The 350z is my first v6, I come from a line of jap motors and I love it, nice little creature comforts, great sounding engine and although it's not turbo it holds its own. The way it pulls really reminds me of my old r33.
Parkers may be the website to help, check the cars out and there's an owners review section too