Well according to the links posted, IS vs AS is about 7bhp and a small diff in torque. The RS is a different story obviously ;)
Coming from a 96 Civic Coupe(non VTEC, ~110bhp, no torque) though so I don't think an IS will feel slow, at least for a while anyway.
Would be looking for something around '02 for under €20k, closer to €15k the better, can't have everything though.
Still not decided on Lexus though, dunno if it's too razzamatazz for me?