your asking the wrong question. cutting diameter is not nearly as imprtant as total cutting surface. for example Rage makes a 2.3" cut broadhead however Grim Reaper makes the Whitetail Special that is a 2" cut.
now you might say the Rage is bigger but in reality it is not. since that Rage is a 2 blade and the Grim Reaper is a 3 blade, the Grim Reaper has a larger total cutting surface area. the Rage's total cutting surface area is 2.3", same as diameter, because it is only a 2 blade. the Grim Reaper has a 3" total cutting surface because it is a 3 blade.
now, due to that Rage only having 2 blades, it will get better penetration due to less overall blade resistance. using the Grim Reaper will take more KE and MO because it has more overall blades to push through an animal.