fwiw, @Stan Galat, the 4-inch saw seems to be ovaled slightly. It's not "walking." And my issue so far is getting clean and accurate holes in this 24(ish) gauge aluminum sheet, not the 'glass. Still, good tips. Hole saws require more finesse than I at first realized.
The way forward, I think, is for me abandon the scrap pile and crack the wallet for some thin aluminum plate, as the job requires.