The question is : is it safe to install the game on nand if my Wiiu is USA and the game is EUR ? If so, i'll try that to see if the slowdowns are less worst.you can't play from external hdd with the update in nand... at least doesnt' worked for me... game doesn't recognized the update when tried to execute it, cause i have white wii u and i can't install the entire game in nand.
if anyone knows how to play with the game installed in external hdd and update in nand please let us know how.