When two boats share the same hull type — in this case both the Sundance K16FLX 2013 and the Sundance NX21 2011 are modified vee 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 Sundance NX21 2011 measures 21,1 feet overall (2011), giving it roughly 5,3 additional feet of deck space compared to the Sundance K16FLX 2013 at 15,8 feet (2013). Weight tells a clearer story for trailering families: the Sundance NX21 2011 tips the scales at 185 lbs — 117 lbs less than the Sundance K16FLX 2013 at 68 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 150 hp, the Sundance NX21 2011 has a 100-hp advantage over the Sundance K16FLX 2013's 50-hp ceiling — enough to notice on acceleration and at cruising speed, particularly with a full passenger load. Fuel capacity breaks the other way: the Sundance NX21 2011 carries 45 gallons versus 1 gallons in the Sundance K16FLX 2013. On a lake day that's negligible, but for coastal cruising or long reservoir runs the extra range matters.
For family outings this is probably the sharpest distinction between the two. The Sundance NX21 2011 is rated for 8 passengers, while the Sundance K16FLX 2013 caps at 4. If you're regularly pulling extended family or a group of friends onto the water, the extra seats on the Sundance NX21 2011 could be the deciding factor.
Bottom line: Choose the Sundance NX21 2011 if your priority is putting more people on the water — it handles 8 passengers and at 21,1 ft it has the deck room to back that rating up comfortably. The Sundance K16FLX 2013 is the smarter pick if you want a lighter, easier-to-trailer boat rated for 4 that costs less to run day-to-day.