That shows a misunderstanding then. All vessel's supercruise performance is the same. Your acceleration and deceleration (for set throttle) is determined purely by gravity. You can always catch-up at the end of a journey, which is what NPC pirates do............ Also, SC is a bit hard to figure since I can Never over-take other ships, they always accelerate far ahead of me even if I think my ship is faster than their Sidewinder. But NPC can always easily catch up to me in SC... I think overall FD make NPC follow the same rules as players but in case of SC I have a pretty big doubt about that.