RVR 5th speed gearing = 0.666
GSR 5th speed gearing = 0.666
EVO I-III 5th speed gearing = 0.617
The EVO 5th gear is longer than RVR/GSR and will give you a bit lower revs at any given speed. So DONT change 5th gear in your already EVO gearbox!!
If you had an EVO gearbox and wanted to bring the ratios closer together from a 4th gear to 5th gear change, then you would put a RVR/GSR 5th gear in it. In which case you will need both 5th gear and the 5th gear sub gear that mates to it. You would do this change only if you had a circuit car. The evo gearing is pretty crap for highway cruising from the factory so you don't want to make it worse by swapping out the 5th gear for an even more unbearable one.
If you had a normal RVR/GSR gearbox then you would put an EVO 5th gear in it to make the legs even longer in 5th and to reduce the revs in 5th gear whilst highway cruising.
But because a normal RVR/GSR already have a different front diff ratio due to less teeth on the crownwheel, all the gears are already spread out more than an evo and make regular street driving more pleasant for a mass produced car.
Edited by EVO-00X, 24 January 2015 - 10:50 PM.