Have both (including a second 800 for backup and dedicated salt beach use and a 600 for family beach excursions).
The 600 IS a solid machine and if thousands of detectorists at one time considered the AT Pro a capable workhorse detector for the masses, then at the same (or better) price point, the 600 literally blows the AT Pro (and AT Max for that matter) out of the water IMHO.
However, I found whenever I used the 600 for beach or backup use after having primarily used the 800, I really missed the User Profile button which does not exist on the 600. I use that frequently to quickly switch between modes on the fly or when interrogating targets (I like to occasionally hit iffy targets with a second mode, different than the one I am searching with, often gold mode or a deep single frequency Park/Field mode to see if I can make the signal pop or confirm likely iron).
Also, to further clear up a misconception, the 600 DOES use the exact same MULTI IQ frequency SPECTRUM (roughly 5 through 40 khz) and Multi IQ signal processing as the 800 for the modes that are common between the 600 and 800. Neither the 600 nor the 800 transmits all five frequencies into the ground simultaneously in Multi IQ, it most likely transmits two or at most three of the five base frequencies and uses the properties of frequency multiplication and harmonics to roughly cover the spectrum from 5 to 40 khz that it monitors on the receive end. Electromagnetic physics shows that you would need ridiculously high transmit power to have enough energy to transmit all 5 discrete frequencies into the ground simultaneously to get the same signal response amplitude of a single frequency VLF detector. The two or three base frequencies used are dependent on the mode selected so that the frequency weighting is consistent with the desired primary target objective of the search profile/mode. This has been verified independently by folks who have hooked up oscilloscopes and frequency analyzers to their Equinoxes and ML implies as much in their Multi IQ literature posted to their site.
I suspect that in the name of keeping things "simple" and perhaps with a little spin doctoring from the marketing department to differentiate between the 600 and 800, ML correlated the five discrete single frequencies that they selected for the Equinox 800 single frequency modes to the multi IQ "cloud" diagrams in the manual and marketing materials. Once they decided to remove 2 of those 5 single frequency options from the 600, then confusion reigned supreme regarding the 600 and 800 multi IQ capabilities. I blame ML for trying to get a little too cute with the Multi IQ explanations and causing confusion because of what they refuse to reveal about how Multi IQ really works to protect their intellectual property from the competition.
In my opinion, instead of stripping some key features to artificially create a perceived "streamlined" 800 with the 600 (it is really no simpler to operate than the 800 because they are BOTH simple to operate), they should have just provided the same 800 detector features in both and just differentiated the models by excluding the wireless accessories to provide the price deltas. I don't see how you actually make a cheaper to manufacture detector by excluding some performance features (e.g., non-ferrous tone breakpoint customizatons) that are simply implemented in software with exactly the same hardware and electronics, but I digress...
Regarding 800's "gold mode", well I have never had the opportunity to use it for prospecting and as Jason has stated above, it is a completely different animal in the way it processes signals (not just the frequencies it uses) and provides the audio information to the user in a much different manner than the other "standard" modes on the Equinox and I have found it to be a killer in both highly mineralized or even mild soil conditions in thick iron to pick out some sweet deep keeper relics and coins and have even used it to success for jewelry on dry sand at beaches. So if you don't think you need gold mode because you don't prospect, then think again about how that mode can be used. On the flip side, the "2" modes on the 600 and 800 are optimized for mid-conductive targets and you will snag plenty of yellow stuff out of the ground using those modes on the dirt.
Having the wireless audio hardware already in the 800 box rather than having to get it from third parties or from the overpriced accessory store is a bonus and little things like being able to modify the non-ferrous tone breaks and tone pitch, variable brightness backlight and the ability to manually select the quietest EMI noise cancel channel should not be overlooked.
The 600 is a GREAT machine and a great value and has and will make for some happy detectorists, but the 800 just takes it to another level IMO. Sometimes you don't know what you are missing until you have used both.
HH