Here's a sales comparison of the latest GT vs the latest Halo:

The last "main entry" or numbered Halo, Halo 3, hit 11.60M, was a current gen game and is the best selling game in the series. GT5, the best selling current gen GT, is a few million off this number and though it's expected to sell at least another million, it still won't get close to 11.6. Gran Turismo has been known to sell up to 15M (GT3), but that was all the way back in 2001 on the PS2.
So, let's say GT6 was releasing this year on the PS3 of course, would it have a chance at outselling Halo 4? (Let's also say they have similar marketing in terms of budget and quality).
Source (sales data)








