If the slowdown happens during the opening karaoke, try using
xy-VSFilter
(If you followed that guide, make sure you run regsvr32 on the xy-VSFilter VSFilter.dll, un-check auto-load subtitles in MPC-HC, and set DirectVOBSub to preferred in MPC-HC external filters).
Ironically, we were just troubleshooting someone's problem with [UTW] Fate/Zero 05 over at the
CCCP forums. So far, it seems xy-VSFilter + FFDShow gave the best results, and gommorah is presently trying to improve the lackluster performance when using threaded-VSFilter.
Other things you can try:
Disable the P010 format in LAV Video
AND/OR
Use FFDShow instead of LAV Video (should be slower but you never know)
AND/OR
Use the Overlay Mixer renderer in MPC-HC
OR if all else fails
SMPlayer2