So much ignorance from both sides.
OT: Both should do at least 9mi. It'll take GT longer though. It took GT4 4 years to hit 10mil. I expect heavy bundling, so GT5 might do it in 3 years, maybe 2.5 years. If Halo 4 (or whatever) releases in 2 years instead off 3, then Reach's sales probably won't be too high for GT to catch up to.
I think it all comes down to when Halo 4 releases. If 2012, then GT5 has a fair chance. If 2013, it'll have less of a chance. And it depends on when GT6 releases. You also have to consider when PS4 and 720 releases. I expect the PS3 to have a longer lifespan than the 720 by 1 or 2 years, therefore giving GT5 an advantage.
I give it a 45/55 chance of outselling Reach. If it does happen, it'll happen in late 2012/early 2013.