It's not clear from the log what's happening. If I make the sum of the time spent server side, I count 267000ms, so about 4:30. Which means there's more than 5 minutes unaccounted for.
Is it possible that the client or network is slow for some reason? Also did you enable gzip compression on nginx? As that could possibly make a small difference.
By the way are you still getting the same results with nginx webdav?
