Here we go.
You can see why I say 12kHz is the best all around Freq IMO for moderately sized targets. (Air test of course, barring moisture, mineralization, EMI etc.)
For silver dimes and quarters, 12kHz is the deepest, however once you get into the really big silver the 4kHz finally shines. Keep this in mind, a big copper/silver coin colonial digger would want to use the 4kHz while a guy in the UK digging hammies (or half-dimes and fish scales locally) might prefer to use the 12kHz or 18kHz
If you want gold alloys, or are looking for aluminum or zinc-ish type targets, then you will want to go with 18kHz for sure.
Higher Freqs also "feel" better, separate better so definitely use them where you can.
8kHz and 18kHz have about the same depth on a silver dime, however the 18kHz sounds better in the field. Air-testing they behave a little more similar. This is just an example as 12kHz is deeper the 8kHz and 18kHz on a silver dime, but say you couldn't hunt 12kHz for some reason, you would have to choose between these two.
I asked Calabash about detecting with sub 2 reactivity, maybe he will chime in in a bit, however I have found as I'm sure others have that I prefer to hunt with higher reactivity, just as I prefer to hunt with higher frequencies, that's when the machine feels the best. This is part of the reason why I like12kHz and a reactivity in the 2 to 2.5 range as a good starting point, the machine still feels pretty good at these settings.
You may also notice from the charts that reactivity has more of an effect on one target vs another, depending on the Freq. Reactivity makes a bigger difference on larger objects. Also the depth seems to advance non-linear as you go lower. Going from 5-4 on a silver dollar might yield a 1/2" while going from 1 to 0 you may gain over an inch.
The reverse is true if you look at the 18kHz silver dime. Going from 2.5 to 0 reactivity doesn't gain you much depth at all, comparatively speaking.
The ruler is 15" for reference. 11" Deus coil.
For 9" coil users, subtract around~1 1/2" average from these depths.