For starters in Airsoft DBOYS its an excelent brand and its SCAR airsoft rifles in my personal opinion are the best. Honestly DBOYS are not the best Airsoft guns in the market, specially for their quality and their internals. I dont know if in the past four years they have improved in something. If you are going to look of a reall power you wount find it in an internal DBOYS gearbox, The SCAR rifles comes with the version 2 that its the same as all M4/m16s and even the masada. probably the SCAR will come with a M100 or M110 spring that will give you around 330 to 250 FPS. To reach the 380-400 or more FPS you will need a M120 spring, new metal bushings and a 9,6V X 1600 AMP Battery. I have to do the same with my DBOYS M4, new metall bushings, new M120 Spring and a new battery. after some time may be you will need a new piston and a new head piston. a friend of mine who bought a DBOYS SCAR he bought a new gearbox with M130 Spring and reinforced gears and parts, he run his SCAR with a lippo battery. He is creazy I think he can reach around 450 FPS, that SCAR is just for outdoor games.
The best SCARs in the market for me are the G&G, their quality its outstanding in almost all of their aspects.
the Holo and the amplifier sights are awesome and you will need the, the grip is very practical and the flashlight is just perfect for indoor games.
I hope this will helps.