I used this guide:
2gb Trancend SD, Smashstack (PAL version). Played ALOT of F-Zero GX (my reason for doing the softmod). Installed 16:9 HBC forwarders, all colors, installed Nintendont forwarder.
I also did the Stashstack PAL on my friends WiiU, worked fine there too.
Have not installed any other WADs.
Have HBC been reported to fail on other units running 5.5?
Thanks for sharing, I'll have to try this myself sometime.