Too many variables in play.. one having testing many different machines swing speed can make all the difference. Some like a slower swing , like most minelabs need. Settings for each machine are critical as well. I have seen Calabash's videos and i have very similar results and i can hit a 9 in dime with ease with NOX, Deus, Impact. So can my v3i for that matter. GB is critical for these tests also , because a slightly off or incorrectly GB machines will suck. Also coils play into it, i have a max right now and i know why the guy sold it to me so cheap now with 4 coils... the smaller garrett coil is no good i cannot even get a nickel at 4 inches and it is impossible to GB properly with it on the machine. Stock coils vs aftermarket,, size too matters.
I agree most machines are pretty darn good , especially in a fairly clean environment.