got both.
totally different. gti is a great all round package with terrific practicality, easy to drive (with dsg), fast, and relatively economical.
balance, poise, handling of rx-8 in a different league and no turbo lag in a smooth seamless power delivery. But economy dreadful (best ever in nearly 3 years 22mpg) and driving in traffic a chore because of driveline shunt. in spite of many moans about gti quality it is no worse than the rx-8 in this respect (new alloys, cat, xenon self-levelers etc)
but I love them both....