Yeesh, there seems to be a alot of erroneous info in here. I will not claim to be an expert on this knowledge by any means, but here are the following things I have heard to be different or seen/studied myself:
1. Powerplants only "power on" a module, like a weapon. Powerplants also play a role in heat dissipation/management (efficiency rating). Going over 100% power usage is possible if you set module priorities for non conflicting modules (like setting FSD Interdictors and Fuel Scoops as priority 2 since they will never be used when hardpoints are out).
2. Power Distributors work as such:
-Weapons - a recharging capacitor to fire weapons from. The better the Distributor, the larger the capacity and faster the charging rate.
-Systems - a recharging capacitor to refill shields from and supposedly other misc components. Shield refill has a low fixed ceiling, so as long as you have enough power to meet that, no more power here helps.
-Engines - a recharging capacitor to boost from. The better the Distributor, the more often you can boost.
2.a. Power Distributor - Power Management: Pip Settings
-Weapons - The more pips here, the faster the recharge. Or more accurately stated, 4 Pips = the max rate given by the module, less seems to be percentage based (2 pips out of 4 = 50% of the module's described charge rate).
-Systems - More pips here does fill the capacitor faster, but for recharging shields, as long as there is enough recharge to keep feeding the shield rechargers, it doesn't increase the speed at which shields recharge. Pip settings DO however give the shields more damage resistance. There are some formulas around on the forums here, Starlighter or something did the study.
-Engines - Pips do fill the capacitor faster and allow more boosting, but to me the main point of pips here is the ships top speed. Over the course of a few different studies, all seem to agree that ships seem to have a "scale" or "window" for speeds at different pip settings that is unique to each ship. For instance, an Asp can get top speeds of 120 at zero pips and 260 at 4 pips, but a Vulture can get just under 200 at zero but only 230ish at 4.
To answer the OP's initial question, the method I use is to take the Distributor spec's from ingame, treat those numbers as 100% or at 4 pips, then scale them for lower settings. For the weapons, I use, again, Starlighter I think, data put together from every weapon, specifically the DPS and EPS values. The formula is something like: firing time=capacity/(Weapon EPS-Capacitor Charge).
