I would probably buy the SB1300 for a 5.5m, you would be surprised just how much weight all the other bits on the boat add up to.
battery, cabling, electronics, flares, spares and anchor etc.
I would probably have been all right with the SB1300 for the one I am thinking of but like making sure I am going to be legal no matter what.
I am still awaiting a decision on underfloor trunk fitted to a destroyer but it is thought to be around £350 if it can be done.
collection is within a week or two but I have actually paid for mine to be built in six weeks or so to be collected on the way to get the hull end Feb/beg Mar.