If you’ve never tried putting a 5-1/2″ hole in a piece of 1/8″ stainless-steel, my advice is to avoid attempting something so mad. However, if you need to put big holes in tough materials, there’s no substitute for a set of carbide hole saws outside of a knee mill, water jet, or EDM, and none of those are easy to find in the average home shop.
Carbide is a machinist’s darling, and the material is superb for this set of 14 hole saws from MK Morse. $125 for the set is steep, but discounted thanks to Amazon’s usual excellent prices. Milwaukee makes a similar set of five hole saws, but a careful user can cut just about anything with a good, high-torque drill motor or drill press. The ability to tear a sizable, accurate hole in just about anything can be a bit of a tall order for standard bi-metal hole saws, but carbide is up to the task.