Greetings. I just came accross this thread so will follow along. I just set up a xl300 G2 in February. First I have to say I am really envious of your rock scape. It looks awesome.
I added a reefmat 500 last week and am loving it after talking bad about them before

I run a jebao dcp 500 as a return and I am running it at 45% right now. I don't really calculate turnover, math isn't my thing. A return for me is more for filtration. I have it set so it seems to be working well with the reefmat. I do run the y outlet and try to sweep the surface back to the weir
I use powerheads for the actual flow This tank is a learning experience for me. It was my first dry rock bare bottom start up using bottled bac (fritz 900)