If you wanna join the mining right now, then you're already too late. The efficiency will drop rapidly when people start buying these GPUs as it's more affordable.
But with the cost of electricity and the fact that you fairly often might need a new card, it's pretty much useless to mine anyways.
Pretty interesting thought that AMD cards are more power efficient than nVidia's when it comes to mining.
What's most interesting for me: These cards are made specifically for mining and they're more power efficient than their gaming counterparts? Then why not make the gaming cards more power efficient as well? I smell some marketing bs right there.