When two boats share the same hull type — in this case both the Zodiac Pro Open 550 2010 and the Zodiac Pro Open 850 2008 are inflatable rigid designs with fiberglass construction — the buying decision usually comes down to a handful of practical questions: how many people are you putting on the water, how far do you trailer, and what does your tow vehicle weigh?

Size is the most obvious dividing line here. The Zodiac Pro Open 850 2008 measures 27,0 feet overall (2008), giving it roughly 8,9 additional feet of deck space compared to the Zodiac Pro Open 550 2010 at 18,1 feet (2010). Weight tells a clearer story for trailering families: the Zodiac Pro Open 850 2008 tips the scales at 3 749 lbs — 2 867 lbs less than the Zodiac Pro Open 550 2010 at 882 lbs. That difference is meaningful if you're working within a half-ton or three-quarter-ton truck's tow rating, especially once you factor in a motor, gear, and fuel.

The power gap is worth calling out. Rated to 350 hp, the Zodiac Pro Open 850 2008 has a 230-hp advantage over the Zodiac Pro Open 550 2010's 120-hp ceiling — enough to notice on acceleration and at cruising speed, particularly with a full passenger load.

For family outings this is probably the sharpest distinction between the two. The Zodiac Pro Open 850 2008 is rated for 15 passengers, while the Zodiac Pro Open 550 2010 caps at 11. If you're regularly pulling extended family or a group of friends onto the water, the extra seats on the Zodiac Pro Open 850 2008 could be the deciding factor.