Very interested in the costs associated with this. Strik3r did some tables up for me and on a 34, given the useless 6th gear, it could work quite well. The top speed for each gear reduces but you get there quicker is the theory.
Speedo goes out too - would be keen if my ECU (Vipec) could adjust.
r34GTR_4.111.txt
r34GTR_4.375.txt
r34GTRstock.txt