By using Wi-Fi between the iPhone and the Opal the speed of the Wi-Fi in general will be lowered. Please don’t expect any speed miracles here.

The big question is why tethering with cable also brings slower speeds. I can’t really answer that, but maybe another forum member has an idea.

Basically, I could imagine that Apple devices are more compatible with each other and that’s where the speed advantage comes from - but that’s just a guess.