The Go-Devil 18 x 54 SD 2011 vs Go-Devil 20 x 56 2006 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.
On paper these two are close siblings in the size department - Go-Devil 18 x 54 SD 2011 at 18,0 ft versus Go-Devil 20 x 56 2006 at 20,0 ft. At 620 lbs and 620 lbs respectively, both sit in a similar weight class - either should pair comfortably with most mid-size SUVs and half-ton trucks, though always confirm your specific tow rating with the motor added.
Both boats share a closely matched power ceiling - 45 hp for the Go-Devil 18 x 54 SD 2011 and 50 hp for the Go-Devil 20 x 56 2006. Real-world performance will come down more to which motor is actually bolted on, its load at the time, and whether it's a 4-stroke or 2-stroke setup.
For family outings this is probably the sharpest distinction between the two. The Go-Devil 20 x 56 2006 is rated for 6 passengers, while the Go-Devil 18 x 54 SD 2011 caps at 5. If you're regularly pulling extended family or a group of friends onto the water, the extra seats on the Go-Devil 20 x 56 2006 could be the deciding factor.
Bottom line: Choose the Go-Devil 20 x 56 2006 if your priority is putting more people on the water - it handles 6 passengers and at 20,0 ft it has the deck room to back that rating up comfortably. The Go-Devil 18 x 54 SD 2011 is the smarter pick if you want a lighter, easier-to-trailer boat rated for 5 that costs less to run day-to-day.