it'll give you a little more fuelling capacity, but the cream injectors are good for about 180bhp at 2.5 bar - it depends on what mods you've done - it will run the car a little bit richer and might give you a bit more power.
oddball did have a 3 bar regulator yes. and oddball also had a full sportex and drilled air box and made a lovely 160bhp on the rollers (average from 3 different rolling roads)
He was very happy with the results, its only a mild increase and cause its a straight swap fitment is relatively hassle free, and of course you keep the rising rate capability (vacuum hose on top) so fuel consumption is mostly unaltered.
3 bar regs were fitted to late C20XE's with newer motronic m2.8, bosch blue injectors, wasted spark distributor-less igntion.
just incase anyone else is reading this, its not an ipgrade if you have the later blue injector engine.