This may not be very helpful, but this is what I've noticed. There are a ton of sparrows that say their speed in 160, yet there are some that seem to be faster than others anyway. In the Scourge of the Past raid, in the sparrow racing phase, I would remain in the middle of the pack pretty consistently. However, one of my clan-mates would start out towards the back of the pack and inevitably end up in the front. This happens most of the time, if not every time, and he uses the sparrow from the raid. So all I can say definitively is to try different sparrows out and experiment with them. Maybe certain sparrows are faster on specific planets or activities.