There's plenty of options. Agreed, I'd start with improved dampers, lowered springs, and also quality tyres. Thereafter, you could look at antiroll bars. If the car is pretty new, the chassis will be stiff, so you won't notice the effect of a top front strut brace; but it's still a good idea, to prevent chassis-softening. It can be noticable if the car is older and flexy.
I'd say look at Eibach Pro Kit springs, with either KONI Sport or Bilstein B6 dampers. Or an Eibach complete kit, the Pro System.
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I have Eibach springs on my GT. It definitely lowers the rear, by around 30mm. Not sure what model GT you have, but on my V6, the front did not lower significantly; I had to have modified the damper-fork connection to achieve a lower front. Different on a JTD/JTS; it should end up lower.
Q2 offers a big improvement in power-down performance. Presuming you have a JTD or V6.