I really couldn't tell you how many sets I did, but I did work on it for almost 2 days (with numerous breaks). I started with 400 grit paper and I sanded it until the base was almost flat, or until the curvature was almost eliminated. Then I switched to 800 grit and sanded until the base was flat. Then I polished it with 1000, 1500 and finally 2000 grit paper.
When I lapped the cpu I skipped the 400 grit all together. I started with 800 grit and sanded until about 80-85% of the IHS surface was making complete contact with the paper. Then I switched to 1000 grit until the IHS surface was completely flat. Then I polished it with 1500 and 2000 grit. The cpu only took a couple of hours.