need some help choosing a gran turismo game?

I'm looking for someone with indepth knowledge of the last few gran turismo games. I had 5 and the traditional races felt similar to gt4 which was my first gt game I got into. But 5 was missing some cool inclusions like 4 had like the classic cars (Ford model t to be exact) and other cool things that made it unique, special, and stand out. In 5 the special event races felt had less attention to or scaled back like in the case of rally racing for instances. It seems based off my memory and some gameplay videos that the rally races in 4 had more quantity and depth than 5. I did enjoy the kart racing in 5 it was a good way to mix up the game and from what I've seen between 6 and 5, 6 is the better one to choose since it offers everything 5 had including dlc. So if someone with in-depth knowledge of gt4 and 6 give me some advice on which one to get.