Ok i have spent a bit more time thinking about this question and i am now 100% certain answer will be no, probably not even close.
The key to the argument is attach ratios as others have mentioned. People seem to be ignoring the fact previous GT's had in most cases x3 consoles to sell to, hence they had high numbers.
For my explanation i will use the biggest selling GT game of all time GT3. A game that sold 14m units worldwide. The last GT game to break 11m units, which is important because Halo 3 broke that figure to. No other GT game has gone beyond that barrier. GT3 had 136m consoles to sell to.
So if we look at the 136m PS2's sold we see 52m were sold in US, which is 38% of sales. 61m sold in Others which is 44% and 25m in Japan which is 18%.
PS3 is selling at roughly the same %'s. 35m PS3's sold, US 14m which is 40%, Others 16m which is 44%, and Japan 5m which is 14%.
So if we look at GT3 sales we see 14m sold. 7m in US, which is 50% of the total, 2m in Japan which is 14% of the total and 45% in others. Which instantly kills one myth raised in this thread, that it will sell more in Japan.
Now if we use those figures we can find out how many PS2 owners from each region bought GT3.
US attach rate was 13%. Japan attach rate was 8%, and Others attach rate was also 8%.
If we take that attach rate into PS3 that would mean 1.82m in US, 1.12m in Japan and also 1.12m in Others.
Giving us a total of 3.4m. That number is the number of GT5 sold IF THE ATTACH RATIO FROM GT3 on PS2 repeated itself on PS3.
So for GT5 to have a chance of beating Reach we have to assume it will need to compete with Halo 3 numbers. After all i selected the biggest selling GT game so it is fair to do the same with Halo series.
360 has sold 40m units worldwide. Of those 40m sold 23m are in US which is 57% of the total. Others is 15m which is 37% of the total and 1m in Japan which is 3%.
Halo 3 sold 11m worldwide. 8m in US which is 72% of sales. 3m in Others which is 27% and 100k in Japan which is 1%.
So with those figures we can find out the attach rates for Halo 3 in each region.
In US 35% of 360 owners bought Halo 3. In Others 20% bought Halo 3 and in Japan 10% of 360 owners bought Halo 3.
Giving a total attach rate of 28% of all 360 owners buying Halo 3.
So if we follow that pattern set by Halo 3 of getting to 11m and copy it into the PS3 we would find.
35% attach rate in US of PS3 would be 4.9m, 20% attach rate in Others would be 3.2m and 10% attach rate in japan would be 500k.
Giving a total of 8.6m.
That is IF WE USE HALO 3 ATTACH RATIOS ON PS3.
So if you look at it logically your see not only will GT5 have to beat Halo 3's attach ratios it will need to beat it by around 25%. Which with the numbers of PS3's available is not going to happen.
The reason Halo 3 sold so well was because of it's american attach rate. 35% of people buying a game is outstanding. The difference with PS3 is it is nearly 10m units behind in US. Which while they are ahead in other regions it is not the right region for GT sales. As pointed out GT3 overall sales had 50% in US. Meaning half of GT5 sales will most likely be in US. If even 50% of US PS3 owners bought GT5 it would still be nowhere near Halo 3 sales.
Which basically concludes for GT5 to win it will need to break all gaming records this gen and do something no GT game has done for almost 10 years, which is break 11m units, whilst beating it's own franchises previous records with 66% less consoles to sell to.
The atach ratio figures are against it. If GT5 even sold 29% attach rate on PS3 it would still not beat Halo 3 numbers. It would need a ratio of around 35%. Meaning 1 in 3 people buy GT5.
Not going to happen.