http://www.gran-turismo.com/us/products/gtsport/

With more than 75 million cumulative sales (*) around the world, Gran Turismo has revolutionized the driving game genre.
The next evolutionary step in this history-making series will soon be coming to PlayStation®4.
Get ready to be taken to new unforeseen heights with “Gran Turismo SPORT.”

That Gran Turismo SPORT will feature highly evolved graphics and sound quality, not to mention a totally revamped physics engine,
should come as no surprise. The true beauty of Gran Turismo SPORT goes much deeper, as it will forever change
the way driving games are seen. It will redefine the very definition of “gaming” and “motorsport

(*As of March 2015)

It would be nice to see someone tally up what we have on chartz as cumulative sales for the series.

So like 5 million games sold in the past two years (including all GT6 sales).

so its afe to assume that GT6 did around 4~ million. probably 4.5 - 4.7 though. PSP is dead, and the only other game left that could possibly sell is GT5. 

GT3 was the pinnacle of the franchise. I love GT but it lost it's way with the transition to PS3.

not really , it run @60fps 1080p on PS3. Bad marketing for 6 and ignorance to technical knowledge by console gamers at the time is the cause. Ridge racer 7 was also 1080p 60fps by the way.

now

GT5 Prologue was the pinnacle. It pioneered the idea of a paid demo.

Not sure it this is serious but here's my problem with GT after GT3. Modding your car was seriously dulled down in GT4 and slowly built it's way back up when it should of been expanding on GT3. Menus are dated, online a pain in the butt. GT5 had licences that you didn't need to pass to progress through career. Career mode dated and all over the place.

There's probably more

GT5 Prologue was good. I think I actually prefered that to the mess that is  GT5