Gran Turismo will rip Halo:Reach new A-hole in both Others and Japan, but will get severly beaten in NA. Overall I'd say GT5 will sell more LTD, while Halo:Reach will have better opening week.
MY HYPE LIST: 1) Gran Turismo 5; 2) Civilization V; 3) Starcraft II; 4) The Last Guardian; 5) Metal Gear Solid: Rising