The Xpress Deck Series - 1756D 2008 is a flat-bottom design and the Xpress XP20 2011 is a modified-V design, so you're likely deciding between two noticeably different on-water experiences. Hull type shapes everything from ride quality and fuel burn to dock handling and resale trajectory.
On paper these two are close siblings in the size department - Xpress Deck Series - 1756D 2008 at 17,0 ft versus Xpress XP20 2011 at 20,0 ft. Weight tells a clearer story for trailering families: the Xpress XP20 2011 tips the scales at 1 190 lbs - 760 lbs less than the Xpress Deck Series - 1756D 2008 at 430 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 115 hp, the Xpress XP20 2011 has a 75-hp advantage over the Xpress Deck Series - 1756D 2008's 40-hp ceiling - enough to notice on acceleration and at cruising speed, particularly with a full passenger load.
For family outings this is probably the sharpest distinction between the two. The Xpress XP20 2011 is rated for 5 passengers, while the Xpress Deck Series - 1756D 2008 caps at 4. If you're regularly pulling extended family or a group of friends onto the water, the extra seats on the Xpress XP20 2011 could be the deciding factor.
Bottom line: Choose the Xpress XP20 2011 if your priority is putting more people on the water - it handles 5 passengers and at 20,0 ft it has the deck room to back that rating up comfortably. The Xpress Deck Series - 1756D 2008 is the smarter pick if you want a lighter, easier-to-trailer boat rated for 4 that costs less to run day-to-day.