Hey all, I'm building out my TT bike anew with an 11-speed set up. I have a bead on a NOS Ultegra R6800 rear derailleur and a very good condition used R8000 RD. There's about a $30 difference, with the 6800 being the cheaper part. I see that Shimano incorporated a "Shadow" technology into the 8000 - I have no idea what that is. Any hoo, is there a big difference in the performance of the RDs? I don't mind spending an extra few bucks for the used R8000 if it will perform a lot better. Thank you!