for good advice you need to post the dimensions that you available to work with, as in, Height, and width and depth of your skimmer area.
I noticed that you said 5" water depth, most in sump skimmers usaully run in at least 8" of depth.
Give some more dims, and someone will be able to help more.
But looking at your sump, I would say that a MSX 160 would be great if you can raise your water level to around 8"