Hello mate!
Got s15 spec R with standart engine, only V-mount and AVC-R setted for 1.0 kg of boost.
If you aren't going for sports, standart gear box will be enogh. Out drifters here, in Russia, damages 5-7 gearboxes per season, no matter OS giken or standart 5-speed from s14, cause 5- or 6-speed gearboxes not ready for agressive using with power over 400-450 bhp.
And if you going to get more power, then you should look for kits for swaping gearboxes from z32 to your s15. I know Mazworx making such kits, but I can't give you direct link to this product, they got unknown problems with their webpage: http://www.mazworx.com/
