The Formula GT in Gran Turismo is no more realistic than the F1 cars in Codemasters games. I say that as someone who hated F1 2012 and didn't like F1 2013 much either (alteast not the modern cars). The problem with Gran Turismo is that the physics engine works really great on street cars and on the lower grip tyres and is without a doubt a much more complex and complete physics engine than what Codemasters use, but by the time you're in the high downforce/grip stuff it starts to get a little funky, or well a lot funky!...
The F1 cars in Codemasters are "believeable" but not realistic in a simulator sense, The Formula GT (which is some sort of 2004 F1 car on slick tyres) in Gran Turismo is a bunch of numbers thrown into a physics engine that gives strange results. It's still good fun, but it feels cheap and plastic compared to one of the real F1 simulations (Simraceway, iRacing, Ferrari Virtual Academy).
If you don't give a crap about any of what I just said then we're in luck, because the street cars drive beautifully in GT, the physics engine in GT6 is a massive step forward (especially the suspension!) and it's in my eyes a driving experience that takes a massive turd on GT5, FM4 and pretty much everything else before it on the consoles.
Sadly the AI in GT6 is like driving against a bunch of half drunk amateurs who seem to think that braking hard halfway around a corner is great technique, so don't be surprised if you find yourself passing a BMW M3 on the outside of a corner in your Renault Clio. But the AI can be nice guys, in the spirit of competition they will slow down for you on the last lap to allow you to catch up, which is nice because often enough you will be starting the race from last place in your Renault Clio, racing BMW M3's and Corvettes where the leading car will be 10 seconds ahead before you're even started.
So if you're used to the AI in Codemasters where you can choose the difficulty up to the point where they will race professional times you will be disapointed, GT6 does not have an AI option in Career mode, in Arcade mode it does but it doesn't appear to do anything, they are still crap.
Now you might think "oh but I want to race online". Sadly the game forces you to play the career until you have got your National A licence, which also requires you to race a good few events, and that aside you will have no money (unless you do the glitch, then you will have money, lots of money).
Should you get the game? I think yes because it will be an excellent online racer, especially in the street cars. The content updates coming every month will mean this game has a good lifespan (unlike Codemasters F1) and despite my issues with the game I think it's pretty great. Can't tell you if you should trade in your games (I wouldn't) but I do think it's worth the buy
PS. Clutch doesn't work properly if you plan to use it.
PSS. I see in your avatar you're driving a Kart. Gran Turismo 6 has Karts. As someone who raced karts myself when I was younger... don't expect too much from the GT6 Karts!
