What supporting mods do you have making that power?
Ideally to get your 320 you need: Decat turbo back exhaust, free flow panel filter(or induction kit depends personal taste) 3 port boost solenoid(UK cars only have 2 ports) upgraded fuel pump(avoid the risk of running lean) PFR7B spark plugs came heavily recommended for me. It seemed to be one of the main criteria when I was being mapped as the first questions he asked were "which plugs and how old are they?".
I have 3" turbo back decat zorst, cosworth panel filter, rcm fuel pump, 3 port solenoid(2ND hand from an import) pfr7b plugs. Here's my map.