Who cares...there two completely different types of games going after two different auidences... The only way GT5 will outsell Halo Reach is if your throw in International Sales figures.. due to lack of intrest in the xbox 360 and FPSes in Japan. So when you throw International sales figures into the mix yes...
But, North American sales figures alone....simple...No.
I mean look at reserved games right now...
HALO Reach is at 325,000 with 14 wks left before release.. with a weekly change of 25,000 units (this number will reach probably 1 million by launch)
While GT5 is sitting at 75,000 reserved titles with a weekly change of 833 even if it reaches over 100,000 reserves which it will... it will still be over 900,000 sales short and by then maybe 1 million plus behind Halo Reach.
A Racing game will not erase that deficit.