Stock gearing on my 1.8 NC is not optimal for trackdriving.  The sweet spot for the more twisty parts of the track is somwhere between 2nd and 3rd.  I remember I solved this on my old NA by adding a turbo which added lots of TQ down low making 3rd perfect for shooting out of corners.

Some time ago I acquired  a EU 6-speed (US version have other 1-3rd ratios) from a 2008 NC 2.0 which was for sale here in Norway.
This will put the gear ratios closer together but most importantly it will change max speed for 3rd from 154 to 134 km/h @ 7200 rpm.  It will also slightly raise the shift point into 4th to 6th which is closer to the sweet spot.  This will be good for the Rotrex as well since boost rises with rpm.
The 6-speed is also stronger than the 5-speed.

Gearing comparison with 5 and 6-speed from www.teammfactory.com excelent gearing calculator:


Cruising at 120 km/h with the 235/40 tires  will be almost unchanged from 3448  to 3524 according to FM's  calculator : http://www.flyinmiata.com/tech/gearing.php


Some pics of the new stuff.
EU 6-speed. I guess it weighs more than the 5 speed but it will be worth it.
 

The trans came without a shifter. I have tried to source a stock shifter as the only available short shifter is known to rattle.  The one I ordered on eBay never showed up so I ended up going for the short shifter anyways.

Since the 5-speed clutch is not compatible (and probably weak) I ordered the an Exedy clutch and flywheel with 54% more clampingforce.

I'll start the job sometime this week.