What is considered the cap (70%) for Defense in relation to Impulse speed?

Also, at what value is it considered "low power" and "high power" for impulse engines?

I did an experiment on my Tactical Escort Retrofit yesterday, and frankly....I'm stumped.

My ship's engine power level is 48/30.

I tested the Omega Force Hyper-Impulse Engines MK XI, and was able to achieve a max speed of 24.80. Okay, I thought this was kinda low for my ship, and I figured it was due to the low power level.

Then, I tested the MACO Impulse Engines MK XI, and was able to achieve a max speed of 24.51 (or something close to that). So, I figured standard Impulse Engines must suck in general.

I finally tested the Jem'Hadar Combat Impulse Engines MK XI, and was able to achieve a max speed of 24.30. Uhh...

To recap, my questions are:
1) What is the impulse speed cap to achieve max defense?
2) What is considered "low power" and "high power" for Impulse Engines?

Clearly, 48/30 is not considered "low power." And considering that I'm achieving faster Impulse with the Hyper-Impulse, it would seem 50 impulse power is closer to "high power" than anything else.

Low Power <40
High Power >60

Combat Impulse Engines work at peak efficiency under 40 Power
Hyper Impulse Engines work at peak efficiency over 60 Power

The concept of Peak Efficiency means the power to the Engine isn't wasted so 40 power to engines will still be slower than 100, but you'll be going faster at 40 with Combat than Impulse or Hyper-Impulse.

The problem I've run into is I can't get my engine power lower than the mid 40's now while this is great for my Omega set Escort (Hyper Impulse) which pushes 62 to engines with a setting of 35 it sucks for Cruisers with Combat Engines that are getting 46 Power with 25 to Engines.

24 is the magic number for extra defense from speed. Faster will not net you more defense.

80% for Escort,
70% for Cruiser
Dunno for Sci. I think same as cruiser.

^this is assuming 9 in Maneuvres Spec, Elusive trait (+10%), and no external abilities like Omega, Subspacemod, Evasives, etc.

I reach 83.8% on my Escort. I believe 51/25 engine power with Omega engine.