Is that the Reef Octopus?
I think I'm gonna go with a DC9000. Rated at 2377gph at the highest setting. Should be more than enough.
Ironically your islands are similar to mine, though you did one thing better than I did which was move them towards the back.
Two thoughts you have some nice tonga rock ...think is on the right side...saw it better in your old pics....try to make use of it.
Move the mountains as far back up against the overflows as possible and towards the back of the tank...I like the higher one on the left.
Third thing ...do what you like haha.