When two boats share the same hull type — in this case both the Nitro 640 2008 and the Nitro Z-7 Sport 2013 are modified vee designs with aluminum 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?

On paper these two are close siblings in the size department — Nitro 640 2008 at 18,0 ft versus Nitro Z-7 Sport 2013 at 19,4 ft. Weight tells a clearer story for trailering families: the Nitro Z-7 Sport 2013 tips the scales at 1 675 lbs — 583 lbs less than the Nitro 640 2008 at 1 092 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 Nitro Z-7 Sport 2013 has a 60-hp advantage over the Nitro 640 2008's 90-hp ceiling — enough to notice on acceleration and at cruising speed, particularly with a full passenger load. Both carry nearly identical fuel loads — 24 gal and 26 gal — so range won't be a tiebreaker here.

For family outings this is probably the sharpest distinction between the two. The Nitro Z-7 Sport 2013 is rated for 6 passengers, while the Nitro 640 2008 caps at 4. If you're regularly pulling extended family or a group of friends onto the water, the extra seats on the Nitro Z-7 Sport 2013 could be the deciding factor.