I currently have 5700 shifters/FD/RD along with a 4600 cassette (12/28), and would like to 6700 cassette (11/28). I was looking at the PB product page for the 6700 cassette, and it says "11-28T size requires use of the Shimano Ultegra RD-6700 Rear Derailleur or Shimano Dura-Ace RD-7900 Rear Derailleur." Anyone know if I can use my 5700 RD despite what the PB site says? I'm curious bc there is also a 5700 cassette in 11/28 that's available as well.