Very nice! Back in the late 90's I had 4 mk2's, quickest was a white SRi with a 2.0 Cavalier SRi 130 engine, which had a re-worked head and a larger cam - was great fun!
I will say, while for daily driving the 1*2's have enough torque to pootle along with, the 150odd lb ft they do have is higher up the revs, and as you say they do need a good thrashing to get the full performance out of them, and especially coming from your Astra it will be a totally different driving experience.
I had throttle bodies, but apart from a cat back exhaust system it was standard. Though itbs do help with low down torque, I did gain circa 15lb ft of torque pretty much everywhere through the rev range, the power came from 4000rpm and above.
I will let you know how I get on with my new 172, which will be an internally standard engine, bar an exhaust system, and matched inlets that I will be matching - it is stripped inside, with stiffer suspension, and im off to Pod in about 4 weeks, I will be very disappointed if I don't get under 14.5