I'm planning on doing a raw power damage build for my Nova, and I'm currently working on getting Blind Rage and Fleeting Expertise. If I were to combine a maxed Streamline (+30% PE) and FE (+60% PE), I get +90% power efficiency, which goes above the hard cap of 75%. If I then equip a maxed Blind Rage (–55% power efficiency), would I retain the +35% power efficiency from Streamline and FE?
I have all three mods and I do spend less energy casting abilities, however I haven't exactly done any testing nor have I decided to max out those mods, but as they are now you should be receiving that 35% energy efficiency. I'll get back to this when I have done actual tests with my warframes.