Howdy, having owned 3 Parkers, most recently a 2016 2520 w/300 then traded on a new 2017 2820 w/T300s, if you are looking to purchase new, go with 300s. Performance will be better, economy likely the same as 250s or better, better resale value. Good luck...
I own one. I love the boat. Has twin 250. I cruise at 24-25 knots. @3600 rpms. Burns 20-21 gal per hour. This is w 5 people. Full of fuel, gear, ice etc. I have about 130hours on mine. Do a lot of offshore fishing. On calm water have had it to 43-44 knots. Great boat.