the gas mileage is kinda a non-issue cause honestly they both suck lol.

RX-8 is 16/22
S2k is 17/23

as far as handling is concerned, they both handle beautifully and they both have 50:50 weight distribution.

One thing that might be a factor is for some reason I think the RX-8 would be cheaper to insure... not sure about that though.