Good job and thanks for the honest review but I just don't agree it's a suitable method to recommend for that material with that sort of thickness.
Sure it may do for a one time job especially if you already had some of the equipment BUT you took your time, used lubricant and pushed your equipment to the absolute limits. If you had more than one to do I think you'd struggle, with a step drill you obviously have to keep drilling consecutive holes to reach the diameter you want putting your drill under tremendous stress. Stainless steel is a pig for blunting tools that's why a carbide tipped tool would always be a superior choice in this situation. I spent a few of my early years as a machinist, hate stainless and once the bit coating is cooked or worn forget about it, well done again for getting it done but it's not one I'd recommend.