Since upgrading to Mavericks, streaming a film from a network hard drive seems to be incredibly slow. It's not the video player (VLC or Quicktime) either.
I have the same issue. I have MBA 2013 with WiFI ac. I use VLC 2.1.0 and latest Free Blu Ray Player to play video from my NAS.
I see lags when playing files of different size 5Gb, 15Gb and 25Gb.
Yes! I thought I was going crazy.. using a dns-325, and just starting to play a video seems to take forever. Immediate change after upgrade to Mavericks.. hoping this gets addressed.