Nitrofueled

Ok so I was bored last summer and got a hair up my butt to build a boat. Well now that I am who knows how many hours and how many dollars spent am looking to power this boat. It is a 26" monohull I built from scratch. I am looking at the HK 180amp esc and a 2100kv turnigy motor with 2, 4 cells ran in parallel. I would like to see speeds in the 40-50 mph zone with decent runtime. from what I read an octura x440 seems to be a good starting point, but I would like to confirm this before I do buy it. Or what is the best method for finding a good prop? Do I have to buy all metal and just try them or is there somewhere that sells plastic versions? I cant find too many a few here and there.