Hi, Forerunner here. I'd like to dedicate this blog series in correcting some inaccuracies the community seems to make a lot and encourage them to remove them when found. This blog will be dedicated to slipspace.
Do UNSC ships all travel at 2.5ly/day?
Answer: No. The vessel that Lieutenant Wagner used to get from Reach to Earth took some five days. While this does total at an approximate close to this answer, it should be disregarded on all other ship articles. The reason for this is because, according to Halo: Contact Harvest, the slipspace drive is not used to accelerate in slipstream space; conventional engines are used, instead. Based on this it can be assumed that vessels with more powerful engines will travel this same route much faster than others. Therefore we cannot use 2.5ly/day as the default for every human-built ship.
Do Covenant ships travel at over 900 ly/day?
Answer: Not exactly. Some fans compared the time it took for the UNSC Pillar of Autumn to get to Reach (approximately 20 days) and, assuming that all human ships travelled at 2.5ly/day in slipspace, concluded that the Ascendent Justice travelling in less than 13 hours meant that all Covenant ships travel at over 900 ly/day. The problem here is that fans have come up with the distance of the Soell system using the false "UNSC velocity formula". Furthermore, yes, the Ascendent Justice could reach high velocities. However, the Covenant did not travel at such speeds, as they believed that using their Forerunner-based slipspace drives to reach velocities that had never travelled at before was heretical.
Up next weak: "Disregarding canonicity debates on Halo Reach"