Forza games have usually a two year develpoment cycle Forza 2005, Forza 2 2007, Forza 3 2009 and Forza 4 2011.  But I go out on a limb and say that Forza 5 wouldn't make much sense as a lauch title for the next MS console so I see Forza 5 coming out next year.  Gran Turismo 5 almost had a six year develpment cycle but I be optimistic and say they can reduce development time for GT6 to about five years so it should come out sometime in 2015.

Devolpment cost are going up for next gen games unless they pull another GT3 (less cars and tracks then GT2) then GT6 will cost substantially more then GT5.

what makes you say that?  GT5 was the anomoly in the GT series.  They pushed out GT and GT3 close to the launch of their respective systems.  I would expect GT6 to be out in 2014 or 2015.

i can see it happening

Turn 10 has more then double PD employees.

Only because GT5 need 5 years to make doesnt mean GT 6 will take the same amount of time. Polyphony hired people too, not only Turn 10.

And for the productiosn costs. Most people dont expect next gen to be much more powerful so i dont expect nexgt gen gamesto be so much more expensive to make.

The first poster who compared it in this thread was the OP

OT: I think it will get close to 10 million this year. Last year it had a bit of help from the bundle in Europe (?) so without any bundles it probably won't quite make it but if it has one it should cross 10 million with ease.

Gran Turismo 1 was released in 1997 the PS1 was released in 1994 I wouldn't say that is close to launch the only GT game that released close to launch was GT3 and feature wise it was the worst in the series it contained the fewest tracks and barely had more cars then the first game.  Each Forza game so far has come out two years after the previous one but I doubt that Forza 5 will come out this year as a lauch title for the next MS system but I'm sure it will be out sometime next year.  The only way GT6 will be released in 2014 is if the PS4 lauches this fall and they don't release GT6: Prologue.

It more like 6 years GT4 was released in Japan on December 28, 2004, GT5 was released on November 24, 2010 in NA and EU.  The average development cycle for each main Forza title has only been two years.  If you want GT6 anytime soon you better hope for a fall launch of the PS4 and hope that they don't release another Prologue.  Also production costs are going up regadless of how much more powerful the next consoles will be.

And lower profits.