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.