To be honest, the only reason I even have two plates anymore is because my double hose has a dedicated plate that's specifically designed for double hose regulators. I used to have 2 steels and an aluminum and my aluminum double hose and had dedicated setups but it became annoying because I'd inevitably end up with too many configurations, even though I was trying to standardize one plate per configuration. That worked great until I wanted to dive AL80 doubles in a wetsuit, or a rebreather in a wetsuit, or a single in a drysuit, or a...., or a...., or a.....
Now the steel is for doubles and rebreather, always in a drysuit, the aluminum plate for my double hose is mated to my 18# wing for singles. That's it. So I gave the aluminum and one steel away and have been happy ever since.
That doesn't mean that's the path you should follow. There is absolutely nothing wrong with your logic at all. And there's not a lick of difference between donut and horseshoe in practical use. I prefer donuts because they tend to be a little narrower, but that's just me being nitpicky. At this point you could just sell the 44#'er and be done with it. You've got the rest of your bases covered. And as long as you can undo a couple sex bolts, or undo a cam band, there's no reason that you can't mix and match whenever you want. Put a set of straps on each and just undo and pull the wing off.
