Im sure much of the information can cross into other chassis.
General Rx8 Transmission Information
Mazda Rx-8 04-current 13B Renesis Gearbox (manual)
1st: 3.815
2nd: 2.260
3rd: 1.536
4th: 1.177
5th: 1.00
6th: 0.787
The most popular "close ratio" conversion i have seen is the miata box. Below is a comparison of the miata box to the Rx8 box given a 9000 shift point and 4.78 final drive (my personal setup).
Now here is the 12a transmission i have currently versus the Rx8. much better!
And also the Turbo II's R type transmission (87-88) compared to the Rx8. Again, 1st and 2nd are similar, but from there on out, for my natural aspiration application, the gearing is superior.