Surfing Waves

Looking to pick up a JS Fatfish, anyone have any experience on this board? Trying to decide between a 5'8" or 6'. I'm 5'8" 160lbs and this will likely be the smallest board in the quiver. I'm riding mostly powerless beachbreaks with the occasional chest to head high day.

I'm throwing three other boards into the mix as well...
Lost RNF 5'10" (tri)
Kechele Stub Fish 5'10" (tri)
Lost Shark 5'10" (quad)

Surely the more volume in the board the better for small mushy days? A 5'8 or 6' might be a bit difficult to ride these waves. But I am not an expert on fishes (far from it) and I've heard they catch small waves pretty good?!

Sorry that was a bit confusing, I have 7'6" for the really small days. The fish will be for 3'+ days, I was going smaller b/c every shaper so far is recommending rider height to +2" in length.

The other consideration.. tri or quad? All of my boards so far have been tri setups so I have no point of reference.