I have driven the s2k and i is pure sex.But i have to admit between the 2 think of it like this.

s2k> very sexy clean and fun as fu** to drive,But every 1 got one
rx8> very rare maxed out and there clean as fu** cheaper on insurance and not to many ppl rock them.

Never driven the rx8 but i must say i might find myself checking 1 out this week just to see how it rides.But they can be made just as sexy as the s2k trust me,and u will get a ton more looks than the s2k considering your rocking something different.