When two boats share the same hull type — in this case both the Nitro 640 2008 and the Nitro Z-9 CDC 2011 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-9 CDC 2011 at 20,8 ft. Weight tells a clearer story for trailering families: the Nitro 640 2008 tips the scales at 1 092 lbs — 877 lbs more than the Nitro Z-9 CDC 2011 at 215 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 300 hp, the Nitro Z-9 CDC 2011 has a 210-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. Fuel capacity breaks the other way: the Nitro Z-9 CDC 2011 carries 55 gallons versus 24 gallons in the Nitro 640 2008. On a lake day that's negligible, but for coastal cruising or long reservoir runs the extra range matters.

Both boats are rated for 4 passengers — a good fit for a family of four or five plus guests. Comfort at capacity is another matter; the longer hull typically means more seat options and better weight distribution.