When I first got my GT, my 18" wheels had almost new Pirella P Zero Rosso's on. It was an immaculate car and already had FSD'S, Eibach Prokit springs and a Momo upper strut brace, so I had to buy it. I was surprised after driving it home to find it quite harsh, fidgety and generally a bit scary. The suspension was really hard and I considered selling the car, I mean I'd be driving on the A1, hit an expansion seam and the vent mounted phone holder would go flying. I wouldn't even feel confident doing 60 on country lanes.
So I thought I'd try new tyres first, got the. Michellins and took it to Autolusso for a full alignment. Got it back and it aw just such a different car, it's my little Bentley now, way, way better than my 159 TI ride and it didn't ought to be.
I had a twin spark 156 SW, results could be totally different to a V6, but I had B6 or B8 with Eibachs, played with alignment, but after about 2 weeks it all came off, brilliant on long fast bends, but unusable around town, sub 50mph. Changed to KYB excel G's, they worked okay, unremarkable really, loads of Japanese cars use them, but I wouldn't waste my money on them again.
Bilstein B4 are supposed to be oem replacements. All I'd say is if you want to keep the car for a fair while longer, get it right, don't try and save 2 or 300 quid, it's nothing over the life of car.
I'll bet you a fiver you don't buy FSD'S.
Oh, I do have a set of front original 2007 GT V6 springs, dampers and top mounts all built up, also have the rear dampers and I think the top mounts (no springs for the rear, used on on my old sportwagon). I bought my car with around 35k on the clock and the FSD'S had been fitted a while before that, so the original stuff can't be that well used. I'd not want too much money, they're just taking room up in my garage.