The IS350 as i said is a nice ride. Thoroughly enjoyable, direct and swift but the ISF is legendary. It is a beast. It has the looks the sound and the muscle. It is a totally different car, ICONIC in my opinion. Even the wife loves getting into it and letting it rip. I have had the privilege of taking it on a track day at Phillip Island and all i can say is that it was a rush and you really appreciate what engineering has gone into it. It was built for it. Put it this way, when you are in a IS350 and a F6 or Clubsport lines up and gives you that (whats this Lexus poxy car) look then you unfortunately have to grit your teeth and let him go, but in the ISF you can look at him and say BRING IT ON!!! And the best part of it is that when they lose and they always do (unless heavily modified) then the look on their faces is Priceless as they say "Ive just been beaten by a LEXUS".
Danny has a point that if it is your daily driver and you are going to buy the original 2008-early 2009 series 1 model then the ride is very hard. If you can go a little bit further and get the Series 2 MY10 model which is what i have then the suspension is a lot softer and it has the Torsen Limited Slip Diff. I use it on the weekends as a family car and i have 2 teenage children.
Worth the 20k mate.