GoW3 hapenned a long long time ago. The last in the series actually was GoW ascention which sold way less and was also a very inferior game. Maybe the series lost a lot of fans over time and with the latets release. Uncharted 3 was release by the end of PS3 era.
I would shoot for 8 million retail + digital, but it could reach 10 million.
But dont think it will be uncharted level of success.
Ascension was poorly reviewed and was the worst game in the series, hence the poor sales.
TC, 10 mil is way too high, I think it sees a nice boost like Uncharted did over the PS3 versions, but not better than GOW2 on PS2.
I predict 5-6mil tops.