I've got the same issue, and have done some searching on the forum a few weeks ago. Based on the number of cars that are doing this, i don't think the cats are failing, i just think that there is a high sulfur content in certain brands of high octane fuel. I think this is leading to the smell when the engine is outputting a large volume of exhaust. However, i can't figure out why this would happen at high speeds AND high rpms, but not at high rpms with low speeds...