Pretty simple really, the DFX is a fine machine in it's own right but not known for pulling real deep coin like objects when compared to the Explorer and or F-75. In my experience, any CZ series Fisher will hunt deeper than a DFX.
For what it's worth, NOTHING that I've ever
air tested even comes close to the F-75 .... but you don't find the goodies in the air
I lived in Pensacola for 25 years, the soil and the beach is almost mineral free, matter of fact, the Whites machines I tried on the beach would always display ( Cannot Ground Balnce ) and would go into factory pre-set GB mode from lack of minerals to balance against !!!
My point is this: I could EXPECT the maximum depth out of any and all machines I ran there on the beach and just about anywhere else I hunted inland and the DFX was no depth monster by a long shot. It did OK but then again I could go just as deep with any medium priced ( $300 - $400 ) unit in my arsenal as I could with the DFX and that should NOT be the kind of results one should expect from Whites flagship detector.
After running the DFX for 11 months or so I gave up on it ever giving me the kind of results I was looking for, and, I couldn't keep from ADJUSTING it everytime I put my hands on it and that's a BAD habit to get in to. I know this reads like I'm beating up on the DFX but that's not my intentions, but hey, you asked. I can say that it handled great, pinpointed great, and I loved the tones that Whites puts into their units.
The MXT seemed to work better for me that any other Whites I've owned, especially since my main interest has turned to relic hunting over the last few years.
Have over 6000 hours with the Explorers, they WILL FIND THE GOODS .... plain and simple,and they will find them deeeep too.
Now the F-75 is one of my absolute favorite 2 machines of all time, it's extremely fast, gives the user plenty of ground and target information, easier to handle than anything in it's class and every bit as deep as a Nautilus, Explorer or whatever within equal coil sizes.
Oh .... and lest not forget about the nice little backlight and battery economy that is 2nd. to none !
You'll do good with either choice, the Minelab Explorer is a fine machine, just be willing to put in quite a bit of earnest learn time to make it work for you.
The F-75 will still take some time to learn but it's easier to understand .... given your experience, you should have NO problem with either
Good Hunting
Mike