The Sea Ray Fly 510 2015 vs Sea Ray SDX 270 Outboard 2018 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.
Size is the most obvious dividing line here. The Sea Ray Fly 510 2015 measures 51,0 feet overall (2015), giving it roughly 21,8 additional feet of deck space compared to the Sea Ray SDX 270 Outboard 2018 at 29,2 feet (2018). Weight tells a clearer story for trailering families: the Sea Ray Fly 510 2015 tips the scales at 46 800 lbs - 41 140 lbs more than the Sea Ray SDX 270 Outboard 2018 at 5 660 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 600 hp, the Sea Ray Fly 510 2015 has a 350-hp advantage over the Sea Ray SDX 270 Outboard 2018's 250-hp ceiling - enough to notice on acceleration and at cruising speed, particularly with a full passenger load. Fuel capacity breaks the other way: the Sea Ray Fly 510 2015 carries 500 gallons versus 65 gallons in the Sea Ray SDX 270 Outboard 2018. 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 Sea Ray Fly 510 2015 is rated for 15 passengers, while the Sea Ray SDX 270 Outboard 2018 caps at 8. If you're regularly pulling extended family or a group of friends onto the water, the extra seats on the Sea Ray Fly 510 2015 could be the deciding factor.
Bottom line: Choose the Sea Ray Fly 510 2015 if your priority is putting more people on the water - it handles 15 passengers and at 51,0 ft it has the deck room to back that rating up comfortably. The Sea Ray SDX 270 Outboard 2018 is the smarter pick if you want a lighter, easier-to-trailer boat rated for 8 that costs less to run day-to-day.