Just for grins you might try

[jrandeck]

Just for grins you might try the free version of Splash Player: http://mirillis.com/en/products/splash.html

I have some clips recorded on my wife’s camera that only play smoothly using that player for some reason.  My previous favorite player for HWA was MPC-HC (Mediaplayer Classic – Home Cinema).  It doesn’t have the best looking interface, but it does its job well.

I don’t use FFDShow or CoreAVC so I can’t comment on how they compare, and I don’t know if it’s possible to integrate the players above into XBMC, but they are worth trying for a point of reference at least.