The only reason Uncharted 3 will overtake Gears 3 is because of bundling. It's undeniable. Gears 3 sold 3m in its 1st week in Sept and Uncharted 3 sold 1.4m in its 1st week in Nov (the holiday season)...so in terms of fanbase Uncharted is still a long way off. Anyway, both are huge franchises and because Uncharted is such a good game I'm sure the bundling will improve its fanbase and subsequently improve the sales of future Uncharted games.
My prediction threads:
Wii U will sell under 40m units (made on 14th September 2012)
PS Vita will sell under 20m units (made on 30th September 2012)
Wii U will sell under 7m in 2013 - I was right