You're making some very good finds, keep it up. I have the 9" X35 coil, but haven't used it enough to determine any favorite operating frequencies for my two custom programs on my ORX but guess they might be in the 15 to 25 kHz range, although I might like a lower frequency with that coil for some Coin Hunting sites. On-site use and side-by-side comparisons will let me decide.
For most of my current use, for City sights or those more remote, I really enjoy my 5X9.5 DD HF coil. I am getting very respectful depth of detection, and doing well on low, mid, and high-conductive targets. While most that I find are in the typical surface to about 5" depth range, I'm having no problem hitting on assorted sizes of coins down to the 6" to 8" depth range.
I based my two custom programs on Coin Deep, and both 5 User Coin and 6 User Coin have the same settings, except:
-> '5' uses a 14.4 kHz setting and '6' uses 31.1 kHz
->[/b] '5' has Iron Volume 'On' and '6' has Iron Volume 'Off'.
On both I run the Sensitivity as high as possible w/o EMI, the Discromination at '7', and Reactivity (which is not "Sweep Speed") at '2' and never higher than that.
Monte