The Pro Line 3400 SS 1999 vs Pro-Line 21 Sport 2007 comparison sits squarely in the category of decisions where specs alone won't tell the whole story — intended use, storage, and long-term ownership costs all factor in.

The power gap is worth calling out. Rated to 300 hp, the Pro Line 3400 SS 1999 has a 100-hp advantage over the Pro-Line 21 Sport 2007's 200-hp ceiling — enough to notice on acceleration and at cruising speed, particularly with a full passenger load. Fuel capacity breaks the other way: the Pro-Line 21 Sport 2007 carries 7 gallons versus 3 gallons in the Pro Line 3400 SS 1999. 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 Pro Line 3400 SS 1999 is rated for 10 passengers, while the Pro-Line 21 Sport 2007 caps at 6. If you're regularly pulling extended family or a group of friends onto the water, the extra seats on the Pro Line 3400 SS 1999 could be the deciding factor.