I personally can't imagine not having a UV filter on a $1600+ lens. Mine never leaves the lens unless I'm swapping it with an another ND, Polarizer, or something else. Get a good piece of glass UV, and whatever performance hit you might take (not much if any in my experience, maybe some more flare, but a hood can fix that), is easily worth it for the protection. I can't count the number of times a UV has saved my ass over the years.