Can I ask why you need to do this please?
Thanks in advance
Two reason. Explorers keep their ships as light as possible, so all D-graded except FSD, usually. I have a pathetic 2D power plant in my Adder, for example. Low quality power plants not only provide less power, they also have more difficulty dissipating heat. D-equipment in general is not only lighter, but also more fragile (as opposed to B-graded modules, which are heaviest but sturdiest). This means that exploration ships tend to be prone to heat damage. As an example, there is currently an explorer trying to crawl his way home with a shiedless Hauler with just a few percentages health left. Just bad luck when jumping into systems with binary stars. Heat is decided not just by the power plant, but also by total power consumed. So you can counter the low-quality power plant by disabling as many modules as possible. I run between 35%-40%, which can help out a lot compared with someone who runs around 70% all the time.
Which modules to disable depend on what they do, ofcourse. Power management is not something that has to be done a lot on the fly, as a fighter pilot would. Explorers often also go unarmed (less weight plus allows lighter power plant). So you can only switch between engines and shields, if you even have shields. So usually people just set their favourite setting and leave it at that the entire trip. Well, the entire trip the power distributor is eating power (and fuel) while being of no use. So disable it. The AFRM should always be disable to prevent it from repairing things you don't want to have repaired. Would be bad news if you sensors broke but you can't repair it as the AFRM spend all its ammo on fixing the cargo hatch. Fuel scope? Don't use it 99% of time, so don't enable it 100% of the time.
Surely a fuel scoop of a certain class and size is the same no matter what ship it is fixed to? The reason I could see scooping taking longer would be that one of the ships has a bigger tank to fill.
It is relation between fuel scoop level and fuel tank size. The Hauler has a mini tank, but a nifty C3 slot. The Cobra has a much larger tank but only a C4 slot, which is relatively worse. Remember that the fuel requirements per jump are different as well, so the absolute time required to scope enough for one 10LY jump is not just based on fuel scoop size, even while a scope of any given size always scopes as much/sec regardless of the ship in which it is installed. It is, ofcourse, a minor point as I'd assume explorers are not in a rush.