i've driven all three of these...
1) the g35 was the fastest, but kinda disappointing and easy too easy to let the back wheels free.
2) the srt4 was a fun one time drive (turbos are great to plaster you against the back of your seat), but is a really shitty car.
3) the rx-8 was extremely smooth and fun to drive, with much more control than the g35, and also more room in the back seat.
Basically, decide whether you want to have fun without killing yourself in the rx-8 with a reasonable back seat.
OR
Go crazy and be all over the place with the g35 and have nowhere to store anything.
P.S.
and with the traction control off on the g35? forget about it.
Test drive them both and go with what you want more!