49er12, I watch a lot of this guy's video's: Metal Detecting NYC (his name is Merril, and he's a bit weird - but very honest and fun, to me at least). The reason I bring it up is that he has the Equinox 600 and he detects around other guys who have the 800 (a guy named "Phil the Nox" for instance), and last year he was comparing the performance of his 600 vs. Phi's 800. He swears that the 800 was getting more depth and somewhat better separation, though it wasn't scientific testing, and it could just be that Phil was more 'in tune' with the 800. If you watch his videos, don't get distracted by his crazy talk of the 'cat gods' - it's all for fun. And if you scratch below the strange surface I think Merril is a really sharp/smart guy.
I haven't used the Simplex, so I can't do a direct compare. However, I believe the MultiIQ technology on the Equinox (600 or 800) is a true differentiator. I have been experimenting with the Equinox in single-frequency in areas of high EMI, and the performance is poor compared to when it's in MultiIQ. I once accidentally left it in 10khz (I'd put it in that frequency under a power line, but forgot to go back to Multi once I was far away), and I still found a button in 10khz - but I wonder to this day what I missed.
And recently I invested in an XP Deus, about 2 weeks before the snow hit NJ. I got to use it on 3 hunts and I got it specifically for some iron-infested sites. Although the Equinox is an outstanding coin shooter and it's good in iron-infested sites, I was digging A LOT of iron signals that sounded like they should have been silver coins on the Equinox. In one of those same sites that I'd hit with the Equinox I pulled out 3 more buttons with the Deus in an hour of detecting while not digging as much false iron signals, so I think the Deus will do a little better at a few of my tough sites.
Finally, before Minelab raised the price on the 800 I would have argued that getting the 800 was the better deal. But now I think they made it easier to be satisfied with the 600 (and maybe that was why they adjusted the prices the way they did). If you can still get your military discount $550 for the 600 with headphones then that's a steal.
Oh, thank you for your service.
- Brian