I have it pretty easy here in the Carolinas. Most bottom is sand and a Fortress does just fine. Never had a dragging problem. Fortress is one or two sizes up from recommended size, I'm sure that helps.
Now down in the Keys, it is a different story. Bottom there is often a layer of eel snot of varying depth on top of absolutely flat caprock. I've had a lot of trouble dragging there. And so have others. One night a front was coming through and I chose to rent a slip. It was a good idea. That night was full of folks screaming on the vhf as all sorts of boats were dragging around. What a mess.
I don't know what anchor (or two) would work in that stuff.
Actually Ski, it was anchored off the west side of Boot Key for two days in sustained 20-25 from the ENE that I was thinking of when I wrote this in Post #6, the closest I ever came to dropping the Danforth :
I had the big Danforth that came with the boat rigged and ready to drop at a moments notice. Almost did once or twice, but we weren't moving so didn't; plus the next landfall if we dragged was Cuba a 100 miles or so away in one case.
Another place down there we did fine in bad conditions was in Newfound Harbor on the north side. As we were coming around to drop, a guy radioed us a said "get a good set, we had a catamaran come whizzing by here this morning".
The only real tricky spot down there, which was also our favorite, was Bahai Honda. The current does rip in and out of there, you have to be real patient. My avatar picture was taken by another boater from the old bridge as we were coming in once, nice story there, they turned out to be in the American Tug shown to the right in this picture. Got a knock on the hull later that day and the guy in his dinghy handed me a print ! Became good friends.
So what ground tackle did you have? Other places we anchored down there that come immediately to mind, though typically without real bad weather, were off Cape Florida (Key Biscayne), Elliot Key, Pumpkin Key, Tarpon Basin, Rodriguez Key, Islamorada (Lorelei's), Lingnum Vitae Key, Fleming Key, Niles, west side of of Newfound.