you really want to be careful what you're doing here, and who's advice you follow.

the standard chip as mentioned is programmed to run 9 psi boost. it has been mentioned that 12 psi can be run with a standard chip, but is this a peak of 12 psi that you typically get at about 3 - 3500 rpm (and is allowed by the amal valve when running a held boost of 9psi), or is Tiff saying that it is safe to run 12 psi held right up to the rev limit? It may well be on some, but without checking it on your particular engine I wouldn't want to risk it. For example, if your fuel pressure is down for whatever reason, or injectors a bit dirty and not flowing well, you could do some serious damage.

it can be the case that you can get away with running a certain amount of boost in the lower gears as it quickly goes through the revs, but if you do it held flat out in 5th gear, the temperature in the combustion chamber can gradually build up until you get problems with melted pistons!

if you don't really know what you're doing, best to leave it at standard. i would also advise against just going out and buying upgradekits to run 'stage 3' or whatever (you can buy a 3 bar MAP sensor, green '803' injectors and a chip "mapped to suit"), but if you don't fully understand it and don't have the necessary tools to check it (such as measuring the emmisions levels, air/fuel ratio, exhaust gas temperatures etc, etc) you could end up with severe engine damage.

as a fellow cossie owner, i'm just warning you so that you don't make the mistake that so any have made before you and just get tempted to wind up the boost in the search for more power.

keep it standard and reliable, or if you want to tune it at all, either fully research it and get yourself the proper tools (expensive), get it done by a pro (not so bad), or have it blow up you (breaks your wallet and your heart).

at the end of the day, a standard cossie is a quick car. trying to get slightly more power out of it by slightly increasing the boost is not worth the risk IMHO. either get a new chip or remap and proffesional setup for higher boost, or leave it standard.

as i advised before, that rs500 i/c is not helping you at all at this boost level. i would replace it with a standard 2wd (about 20 quid) or 4x4 (about 80 quid) i/c that will cool the charge just as well and give you a better response. keep the rs500 i/c for later in case you start to run serious boost and need it.