I think most will say a 9.5 will be ok. I played it safe and got a mag7 for my megaflow but I thinkg it could handle more.
You can also widen the teeth of the overflow which will increase flow.
*180 gal Display, 100 gal basement sump, 33 gal refugium, 3x250 MH, 2x160 VHO actinics, zoos, some softies, LPS & lots of acros and other SPS.
*100 gal prop tank plumbed into main system w/ 2x96 PC lights and 1x150 MH,