Try to find a decent specialist if you can as opposed to main dealer as they charge the earth and aren't usually as passionate about the older cars as we are.
I run a standard cat...free flow centre section and a Sebring back box, K&N 57i induction and a AmD chip and remap and have RR figures of 172bhp and 154ft/lbs on my 16v...so with a decat you should be up to 175-180bhp....and a bit of luck 
So are we all invited over for our holls then 
If ever you are over here Simon then you're welcome to stay.
We may have a distinct lack of specialist information on specific European models but it is countered by the extraordinary driving roads (4 million population in a country 15% bigger than the UK) and fuel at half the price of England. I also only pay a hundred of your English pounds for fully comp insurance, no alarm needed and the car parked outside. None of those benefits will find my missing 50 horsepower though.
As an aside I drove four 16valve 5 door GTI's when looking and all of them had very similar performance to mine making me wonder if Japan (country of import for all of them) has a model specifically tuned (detuned?) for that country, any thoughts?