I really like jetpacks, but sadly, IC2 features not many. Other mods (e.g. SimplyJetpacks) inspired me to make this suggestion, so here is my suggestion:
In the following, I will use "normal" as a constant. It means "the standard Electric Jetpack as it's in IC2 in the newest experimental".
The "Nano Jetpack"
Recipe: X
The Nano Jetpack should fly 1.25 times faster than the normal one, and have a storage capacity of 1M EU. It should consume as much energy per tick as the normal one does.
The "Quantum Jetpack"
Recipe: X
The Nano Jetpack should fly 1.5 times faster than the normal one, and have a storage capacity of 10M EU. It should consume as much energy per tick as the normal one does.
Balancing
The Quantum Chestplate should require the Quantum Jetpack in it's crafting recipe, and fly at the Quanutm Jepack's speed too.
If the Jetpacks feel too overpowered in-game, it would be a good idea to nerf them (or using a config option) as follows:
Electric Jetpack: 0.75 times normal flying speed
Nano Jetpack: 1.0 times normal flying speed
Quantum Jetpack 1.25 times normal flying speed
The Biogas-fueled jetpack's (this one: 
) speed should remain untouched!
The textures I provided here are just a result of me having too much time. However, if this would make it into IC2 (or an addon), feel free to use these textures if you want!