In my opinion - and from what I?ve read the gs430 is the way to go if it between those two models. I was/am a huge fan of the 2nd gen. But personally as in the previous gen - which was a competitive value- people boosted the horsepower and handling even more to make it great. The new gen- they did not even change gs430 horsepower. A huge mistake. Plus they?ve gone to the darkside like too many brands and made styling too bland, at least from the side :!:. This is we opted for a german make even though we surely prefer more japanese alternatives- german cars are number 1 for looks, perforance "ultimate driving machines".....
If it were me getting a car in that price range I would get a 2003 m5, or even a 2nd gen gs430 then you could turbo it.