First off, good questions.
I am using the stock 8 inch coil on my CZ6a's for comparison to the Deus, and using the standard 9 inch DD on the Deus. My 6a's are units I have had for 20 years, and I have tons of time on them, so my ear is trained for CZ use more than any other unit. I have found silver dimes at 10-11 inches here in NJ, in mild soil since the places I hunted are not mineralized. I run the 6a's at 4.5-5 sensitivity most times, and can jack it up, but they are then more prone to iron falsing and there isn't much if any extra depth gain when using a sensitivity higher than 5 for the most part.
I have not had the Deus long at all, and to me it seems it runs best at the higher frequencies, which lean toward hitting lower conductors a bit better than higher conductive targets like US silver. Seems the Deus hits the small hammered silver in Europe great, but I do believe those guys run at 12 and 18khz due to those coins 'acting' like lower conductors due to how small they are.
Testing the Deus in all 4 frequencies in my test garden, it hits the 7-8 inch silver coins ok, but cannot hit the 10+ inch silver quarter I have. Now the caveat is, this is in some of the preset programs so I have not tried to optimize it yet. But some of the pre-sets do run at high sensitivity settings, but I still will try to see if I can squeeze out that quarter. The CZ, with the stock 8 inch coil, hits the quarter hard and repeatable, so this tells me the CZ does better on deeper silver...at least for me and my knowledge base of the CZ and Deus at this time.
Curious to see the results of your testing with the CZ6. Got some crappy weather here now, but I am going to go back out to the test garden with the Deus when I get a chance, and run it in several settings/configurations and see what transpires.