While I too would recommend the 800 vs. the 600 for various reasons (gold mode which I intend to use for relics, higher max recovery speed adjustment, greater range of iron bias adjustment, adjustable non-ferrous tone breaks/pitch (600 can only adjust ferrous region tone breaks/pitch), user profile mode save button which basically gives you an additional custom program memory slot not available on the 600, AUTO AND manual noise cancel (600 only has AUTO) and the included wireless hardware which makes up a significant chunk of the price difference), I need to point something out to clarify/correct something Smokey said above. With all due respect to Smokey and the daily banner finds of which I am not worthy to even share the same site with, but somehow allows me to do so anyway.
Specifically, as far as Multi IQ multi frequency operation is concerned
the 600 and 800 are identical and both use combinations of all five fundamental frequencies (5, 10, 15, 20, and 40 khz) in various programmed combinations to generate the six basic search modes (Park 1/2, Field 1/2, and Beach 1/2) common to both detectors. Multi IQ is the default frequency setting for ALL modes and based on user reports appears to be the best overall frequency mode for general use. The 600 does indeed only have individual frequency mode selections of 5, 10, and 15 khz, vs. the 800 at 5, 10, 15, 20 and 40 khz. But use of individual frequency mode appears to be useful in only a small subset of unusual situations such as EMI that cannot be cancelled out in Multi IQ mode and for use to interrogate targets giving questionable MultiIQ target ID's to help in bottle cap identification, for example (similar to what is done with the Deus, switching frequencies to see if the VDI goes up when it should go down and vice versa, indicating a corroded object). Basically, what I am saying is that since Multi IQ operates at all those frequencies, it would be the frequency mode I would use to hit the sites Smokey is talking about, but instead of changing frequencies, I would change modes which changes the way the frequencies are combined biasing towards the higher or lower side of MultiIQ (based on the mode selected*) to accomplish the same thing. THEN, I would hit it with my Deus HF coil at 58 or 75 KHZ just to make sure I got everything. LOL.
Just wanted to point out that the 600 DOES use 20 and 40 khz just like the 800 in Multi IQ frequency operation...but the relatively small price difference for what else you DON'T get with the 600 easily sways me towards the 800 (especially with appropriate ML price discounts applied

). HTH
* Just to put a finer point on this. The Park and Field 2 modes are biased high towards mid-conductors and small jewelry items (i.e., hotter), Park and Field 1 are biased lower and favor high conductive (e.g., silver) targets (i.e., less hot). Beach 1 (Sand) and Beach 2 (Surf) are least hot so that the machine is stable in moving/variable salt sand and surf. Gold mode, available only on the 800 is a VCO like mode that is the most hot mode of all (understandably so) and is what I hope will kill it in high mineralized soils.
You can read this in more detail in the Equinox manual link posted somewhere on this forum. (Mods may need some stickies soon, hint hint!)