I know this is a dead horse subject and I've seen lots or videos discussing it. That said, in the current version does the Power cube build matter as far as output? I know in earlier versions it was critical.
The only thing power cubes are good for is for docked power reactors. Even there, you might consider long thin docked power reactors rather than cubes. Forget power cubes exist other than that. You will ALWAYS get more power by running the longest possible lines of power through the length, height and width of your ship. Sometimes you need to put some thought into how to get the most non-touching lines into your ship's space. I find it a trivial exercise to get a half million power regen in even tiny ships. I can easily put a million power into a 10K block ship.
If you don't have a part of the interior of your ship looking like this, you are not building for maximum power:
...And each one of those power lines extend all the way to the outer hull of the ship, save 'usually' the last block, which will be hull/armor.
Personally I prefer cubes for docked reactors, because it allows me to bury them. A long thin ship however might find it easier to bury long thin reactors. Burying a reactor behind many blocks of other ship system blocks largely ensures that it will not become undocked during a battle, which would both spell the end of the battle as your energy suddenly drops, but also likely spell the end of your game due to massive resulting lag and clipping issues.
A long thin reactor (over 60 blocks in length) will be slightly more efficient with blocks than a cube and easier to build (just a checkerboard of lines). The longer the reactor, the more efficient it will be compared to a cube reactor. If it is less than 60 blocks long however, it will start to become 'less' efficient than a well built cube.