(Java Minecraft 1.13) What is the max and min elytra glide speed with rockets?

I'm planning on creating an item which when held in the off hand while flying gives the player a constant velocity, like a rocket but passive. To know what I need to multiply the players Motion[], by, I need to know approximately what the max flying speed with the rocket is. I checked the wiki but couldn't find any actual numbers, just that it goes faster than without. I also could use the minimum speed required to stay airborne while flying straight/level with the horizon. I've tried using a repeat command block chain for chatting my position while flying but the numbers don't really make any sense, as they dip and spike a lot, so I'm just wondering if there's a way to get these values non experimentally.