Dremel reinforced cutting disc
Just as another data point, I tried using my hole saw, which up until this point has performed flawlessly for cutting out aluminium lightening holes, however even with copious amounts of lubricant, the hole saw had its teeth shaved in short order. I then resorted to a reinforced cutting disc on my dremel tool, making small cuts just inside the 2" perimeter. Once I had removed the center, I then used the dremel tool cutting disc like an angle grinder and cleaned up the hole, before finally finishing it with some fiber backed strips of sand paper. I was very satisfied with the result, it only used about half of one cutoff disc, and it really didn't take that long. In hindsight I wish I used the dremel method from the start. If you are going to use a dremel to cut the hole, don't forget to wear a respirator when doing the grinding, as grinding and welding stainless releases chromate nasties.
Tom.