[Redshft]

It's my race car, not a street car (so streetability wasn't a consideration) but, figured I'd chime in. I'm running S5 4-port irons, full bridge port with RX8 rotors, e-shaft, stationary gears etc. and a Weber 51IDA.
Full disclosure, I've not gotten it properly tuned, as I can't seem to keep a transmission in the car (I changed it out 6 times in a year) but initial signs are promising. It does work, it seems to be promising power-wise so far.
With S5 rotors getting scarcer all the time, I think more people will start using RX8 rotors down the road, but, there are a few catches.

If you are going to port it, be aware that the side seals on an RX8 rotor are in a slightly different position than the RX7 rotor. So, in my case, my builder needed to tweak the bridge port template a bit as if he used his standard bridge template (which was Racing Beat I believe) the corner seal would hit the port. So, he needed to create his own.
The other thing is, the apex seals lands are not as deep on the RX8 since they have no peripheral exhaust ports and they don't need to be. We had my rotor lands EDM wire cut to accept Racing Beat RX7 apex seals and they fit perfectly.