I have used both 105 and Ultegra cassettes, 10 speed not 11, on the same bike with 2 different bikes. I really do not notice that one performs better than the other. I have done that with 9 speed cassettes also and, in my opinion, the Ultegra shifts a bit faster and smoother than the 105. That could be that the 105 was a fairly well used, but in good condition, cassette and the Ultegra was new. Don't know it that helps with your 11 speed question, just putting it out there.