Halo 2 did 5M in 3 weeks and was at 6.4M in 2 months. Halo 3 did 5M is a little over a week and 8.1M in little over 3 months. Reach did over 5M in September ($350M). 4 was the fastest selling game in the US for the first FY, meaning it was outdoing Halo 3. It did over 4M week 1. The Halo 5 number is also shipped (just like every other number). More @Wikipedia
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