I know volume increase won't be as big as petrol (like the 1 box system that was on my 200sx) but what sort of increase are we talking on straight through? I would like it to increase sporty note and rasp a little but not too much as I have my wee man to drive about and need it to be not too loud....
Are there off the shelf options as well? I notice ragazzon do not list 20v and supersprint list mid and rear sections but front bits are marked in development (but supersprint are a bit expensive)
Personally you may want a 2 back box's then if your carrying your lil man about.
A decat will make the car sound better with a lower tone and improve performance slightly, but technically you wont pass the MOT.
Also a remap with a custom exhaust will do wonders, ud be surprised.