Before chaising your tail on too many things, try other brands of fuel.
Sulpher smell ultimately comes from excess sulpher in the fuel. Sulpher content can vary greatly depending on the refining process and the origin of the crude oil. Here in California the sulpher content is much more highly regulated than in the rest of the country and sulpher odor from exhaust is mostly just a bad memory.
Sulpher smell is agrivated by anything that put excess fuel into the cats. Running rich, ignition misfire are examples.
Rich running cats can ultimately result in damaged cats.
