Powerhead selection

[Reef.Blue]

I am in the process of buying an Innovative Marine 80g AIO aquarium and I am totally lost with what powerhead to buy. I was looking at the Nero's, but I was not sure if I should buy the 3,5, or 7. I tried searching it up to find more information, but I couldn't find anything.

 

[Snoopy 67]

Definitely not the 7.
Someone with experience should chime in.