If you want to go first class go with Ipe. If I had the coin to redo my dock thats what I would use.

X 2

I make a living selling composite decking for the last 12 plus years, seen many come and go. First question are you going to attach cleats to the decking? not all are strong enough.

All the composites will have some very good plusses, but will also have some negatives. One consistant over the years, 20" span is too much, most will be spongy anything over 12" span. Expansion and contraction can be very noticable in most plastic deckings. I have either sold or sold against Trex, Correct deck ( now GAF duralife) tamko epoch now everlast, rhinodeck, timber tech, Nexwood, Xtendex, Correct dock, just too name a few.

My personnel dock is about 1200 square feet, and I used IPE. 1x6 Can span 30" with little to no deflection. Will outlast ALL composites currently on the market, 50 plus years in all weather conditions. Yes it is heavy, and needs predrilling, but because it is so dense it will not absorb water. Ipe should be very close in price to the premium composites (trex transends, GAF duralife ect). After a rain storm it will dry as quickly as concrete or quicker, and if you do not mind a light grey color no maintence needed. Lastly, in 10 years as a decking no slivers, and no damange from walking on it with hockey skates in the winter, very tough stuff.