I lowered my jtdm GT 4 weeks ago, and it looks and handles great!
I used Eibach pro sport springs, but didn't change the shocks due to the cost.
The ride is a little firmer, but it was firm anyway as it has the 18" multispokes on, but not uncomfortable in my opinion.
Only prob i had was the undertray scraping over speedbumps.
I looked at it, and there must be a 2" gap between the tray and the sump etc.
The tray has only recently been fitted at Alfa, as it was missing whem i bought the car 4 months ago. They used a second hand tray too!
Could they have fitted the wrong one, i.e one for a V6 or JTS which mite have a lower sump, or are all GT models undertrays the same ?????.
I've taken it off anyhow this weekend, which cures the speedbump problem, just need to take care over big bumps now(ive got 120mm clearance under the front end), but in my opinion, its well worth doing for the handling and looks, also the steering wheel is more stable in your hands somehow.
I got the car 4 wheel laser aligned afterwards too to make sure, allthough you can't alter the camber/castor on the GT, so a basic 4 wheel tracking shouls suffice,
I bought the springs from Angel tuning, who did me a deal with a 185-190bhp/260lb ft re-map. £390 all in!!!!.
Fitted them with a mate at his garage, not too hard to do, took us 3 hours all in.
Now the car goes and handles like it should!!