One of my good friends road races an RX8 in T3, and it's classed with the S2000 there. Long story short, the S2000 is simply a faster car, but on the right course, the RX8 can run pretty close. They are helping the RX8 out for next year, but whether it can hang with the S2000 on the straights is still to be seen. His is for sale, at Road America next year it really has no hope of winning.
The difference in weight is huge, and at least in road racing, you simply can't get the Mazda close to the minimum required. On the straights, the Honda simply pulls away.