If you're really after max jump range, you can take a smaller A rated power unit to an engineer and have it overcharged.
Be a bit careful that this doesn't increase the mass too much...
Take the power unit in a small ship (I find a Hauler is an excellent taxi), then swap it over in outfitting.
IIRC, my python has a 7A overcharged power unit - sufficient to ensure that I have all the essential systems (FSD, thrusters, sensors) below 50%.
You probably know that a power unit can be damaged in combat - but only down to 50%. So, if you're likely to be receiving damage, make the essential (get out of Dodge) modules priority 1, everything else lower priority.
Eg
Thrusters, FSD, Sensors priority 1
Weapons priority 2, possibly some to 3 (you can't jump with weapons deployed, so they're a lower priority.)
Shields priority 2 or 3 - if you're under attack and your power module is damaged seriously, you can take some ore damage while running...
Life support 2 - 3, you have 7.5 minutes of oxygen and now you replenish by synthesis.
Things like auto repair modules can be disabled in flight saving power.
Fly safe!