With the respec coming up. I have done a few experiments this afternoon to find what some of the skills do for you. Here is what I found.
Engineering Maintainence - only effects skills. I saw no change in power levels with these skills.
Engineering Efficiency - Effects low power levels. for example at 25% engine power is 38.
Engineering Performance - a flat +9 power at all levels with all 9 levels.
All of the skills of each ship type do boost ship performance.
So with all 9 levels in efficiency + performance engines are 48 at 25%.
Biggest thing is with weapons performance at all 9 levels and 1 plasma manifold an Raptor/BOP will be at 125 weapons power. Add Emergency to weapons and 2 eps and you will do serious damage with cannons.