Hey -- thanks for that. I'll pull back and make something a little more sane. I just acquired a lot of crystal malt, so I was looking for ways to use a lot -- but there's no point in doing that only to make something undrinkable. I had in mind that it might be going a bit in the direction of an ESB, or potentially a barley wine, but maybe I'll simplify.
For my English barleywine and ESB I do use ~10% crystal. Those are styles where I'd highly recommend using Maris Otter or the like instead of regular 2-row, as well asEnglish crystal malts, which to me don't taste the same as American crystal, at all. (Though at 75 L ... what kind of crystal do you have?)
To move your recipe towards an ESB, I'd use Maris, biscuit (or Victory) at ~10%, and ~10% of your crystal. Maybe a touch of something (chocolate rye?) for color. To get into barleywine territory, also Maris, but 15-20 pounds of it (for a 5-gallon batch), 10% amber, and 10% crystal. S-33 would be good for either (though when I've used it it's taken forever to finish.) (I'm sure someone will chime in and say these aren't traditional English ale recipes.)
Baltic porter is another style that can use ~10% dark crystal. You can also make a decent dubbel with ~10% dark crystal, though probably not a traditional one.
Oh, and for any of these beers (ESB, barleywine, Baltic porter, or dubbel), Galaxy would be ... very unusual.