ask the same question on www.clubcalibra.org
but i will start them off : they calibra motor is a MUCH stronger unit than the astra turbo, but the awd system can break easily if not treated properly. they are very tunable, with well over 300hp easily reached. they are heavy and in stock form they handle ok, but if you put it next to say. an old wrx, the wrx would better allround (but would cost you a hell of alot more, and remember the calibra turbo was designed in 1990!!)
these days they are cheap, look great for their age and if you find a turbo with a good awd box then you should have a good time. ask more on the calibra sites, in fact i am sure there are buying uides on there if you are looking for one!
i used to have a non-turbo cally, and it was great