Almost full fat then 
Sadly, the 9-5 (almost) never got the 2.8. It only got that engine in the Insignia based "NG" 9-5 that was briefly available from 2010-2011 ish. And by briefly, I mean that I don't think any 2.8's were made in RHD, if there were, it will be a handful of examples.
For the previous one, (98-09) the 2.3 4 pot was as good as it got. Depending on how late the model, you got either 230, 250 or 260bhp.
The auto is (slightly) torque limited in 1st and 2nd vs the manual but neither will do much at the traffic light grand Prix. 30-80 mph is where the meat and potatoes are

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Henry, you might do well to check this gentleman out. His work is excellent:
http://www.noobtune.co.uk/