Streaming an .mkv of 1080p and streaming an uncompressed blu-ray are two totally different things. I can just barely squeak by with a 720p .mkv and light office work on my 411j. But try to stream that .mkv and run a backup from my notebook? Pffffft.
The 413j has a nice CPU - especially when compared to the 411j - but it's still pretty weedy for an SMB.