So... have you? From the cars I've actually driven in real life and driven in GT4 and GT5P, I'm perfectly happy with the way they behave in game. Except for the eerie, skittish feel of the cars on the grass, they behave much as they do in real life... Enter a corner hot and you understeer... get on the power early and you understeer... the amount of grip you get from the tires is the same (as proven in Scaff's experiments on GT4) and the speed is similar (expecting absolutely the same top speed given non-dynamic airflow and vortex modelling... a stretch to expect on the PS2... is insane). This is all on the racetrack, I might add... comparing in-game to on-the-road is frustrating... and it's only at the limit on a proper track that you start to appreciate how faithful the games actually are to real life. The only black marks are that neither has quite the amount of snap oversteer you can generate in real life (due to a physics modelling that's geared towards preventing the car from lifting tires), throttle modulation is extremely difficult with a pad, and tire deformation and physics aren't quite as detailed as PC sims.
Again... in GT4... you could feel the difference between an Acura RSX and a Honda Integra... and it wasn't just the weight... you could
feel the difference in tire grip and suspension calibration.... and these are (according to the whiners who complain about GT's car lists) ostensibly the same car. GT4 and GT5P are some of the few games you can pop into your console and pick a couple of random cars and spend hours driving just to get a feel for the differences in how they behave.
Hey i play shift aswell, you just have to take it for what it is, an entertaining arcade racer.
I do. And I think it does that quite excellently. Unfortunately, unlike in GT5P, you can't turn the "arcade" part completely off... which makes realistic driving annoying, especially if you're prone to accidentally inducing 4-wheel drifts (I swear... I was trying to race clean!

).
Just so you know, the vast majority of people who play GT5P, play in standard mode.
Now they have Shift. Which they should buy. Because Shift is a lot better than GT5P Standard. It's a shame... with the basic physics engine it has, with a few gameplay tweaks and the elimination of the "Shift bounce", Shift could be a contender against both Forza3 and GT5 as one of the "big guns" in the console sim market.