I've got monster hunter tri (pal) working flawlessly (no freezes so far and able to change name etc). Using a eur wii with 4.1. Also wd attached hard disk.
Using:
Cios rev19 (ios250) using base ios37 (I also have rev19 on base ios57 (ios249), but that causes the screeching black screen upon choosing a game mode).
Running game through configurable usb loader with ios250 selected (the rev 19 base ios37) and the rest of the settings set as default.
Hope this helps anyone.