I think RXS may well be a "straight line jockey" as i mentioned earlier.
Its sounds like you are missing the push from the turbo that you are used to in some of the other cars you mention. The Z engine will only show its best when you use all the revs, they is no point driving it around at 3k rev and complaining its slow.
If you really want to fall in love with the Z, get booked onto a trackday, turn the TC off and drive it properly.
Alternatively, sell the Z and ride the low down torque in your vectra