In the films such as Attack of the Clones and a New Hope we see ships leave the planet's atmosphere in extremely quick time-spans. When it comes to propulsion technology that uses fuel to push itself off the surface of a planet one needs to be mach 33 to escape the pull of an Earth-like planet. During the battle of Yavin the Death Star was moving around the gas giant, while the X-wings pretty much reached the Death Star in less than 5 minutes. The distance between the Yavin and its Moon for the hell of it I assume is around the same distance between Earth and the Moon, which is 384,400 kilometers. Divide that number by 5 since I'm going to say it was exactly 5 minutes. Assuming that every minute the X-wings traveled 76,800 Kilometers every minute, that would make them 3,762 times the speed of sound. And that's REALLY low-balling since all I'm taking into account is them just reaching Yavin, when we actually saw them they were already halfway done crossing it and THEN the timeframe of LESS than 5 minutes for reaching the Death Star was stated, in the films they literally crossed the previously mentioned distance in a few seconds, I've seen calcs that put the X-wings cruising speed at around 3 percent the speed of light. Mach 3,762 is 1,279,080 Meters per second. 1% of the speed of Light is 2,997,925.