Gearbox wise alot depends on how you drive it, i killed a 5 speed on the isle of man at 280bhp (cant remember what the torque was at the time) and track work will not be easy on it. PPG, Albins or similar will do the job or a 6 speed as mentioned. Word of warning with the 6 speed is it adds alot of weight, 50-60kg iirc
As well as the above mentioned items worth looking at oil cooling as well, after market kit (mocal or similar), make sure its thermostatically controlled though. Also i'd look at sacking off the standard ecu and chucking a syvecs on it. Not cheap, but much more capable ecu, plus when you come to sell it on will hold alot of its value. Will need to sack the MAF as well (syvecs will do that anyway)