I've been noticing that even with emerald jetpacks the vertical hover speeds are painfully slow, even slower than vanilla creative flight, I've developed a formula to keep the feeling of fighting gravity while going up and still move at decent speeds. I've pre configured it in the zip for you.

speedHoverAscend = speedVertical
speedHoverDescend = speedVertical + speedHover

jetpacks.zip

These speeds are super rough