I'm now leaning towards a custom 4.0 Vado where I put in the Tero 5.0 granny gears
You certainly mean Tero X 6.0 gears. You cannot do it as Tero X 6.0 is using a 12-speed cassette but Tero 5.0 and Vado use a 11-speed cassette. The difference is as fundamental as it is not doable. However, you can easily replace the chainring in Vado 4.0 with a 38 or 36T one to change nature of the drivetrain from "commuter" to "alpine"
Now, it is not the stronger motor is automatically less economical then the weaker one. Think of two cars of the same make/model equipped with modern engines of different capacity. The bigger motor allows you accelerate faster and possibly get at a higher speed, especially uphill. However, when you are driving either of them at the same speed on the flat, each of them basically consumes the same amount of gasoline per mile.
More Newton-meters means higher Motor Peak Power. You simply have more power "under the hood". However, Specialized assistance tuning that allows you set Assistance Factor (mechanical Watts of the motor per Watts of you leg power)
and Max Motor Power limiter will control how much of energy is taken from the battery. For instance 35/35% assistance on my 90 Nm Vado 6.0 gives approximately the same performance and battery consumption as 80/80% setting on my 35 Nm Vado SL. You are free to set the assistance as you please, especially with the MicroTune feature of the new Mastermind e-bikes (you are tuning the motor with buttons as you ride). (Thank you
@Nubnub for your post!)
But with the 90 Nm, a press on the Turbo button uphill would be a pleasant surprise for you. Just because you would have 565 W of mechanical power under the hood (about 715 W of electrical power), and 4.1x Assistance Factor.
The third thought is that I now ride a recumbent where you cannot stand up and pedal. So when you hit the long 17% grade the only option is to walk to bike up the hill, which was a real drag when I had clip on shoes. Perhaps I could even get up my hill with a 3.0 if I stood up while pedaling on a normal bike? Even worst case scenario the walk mode would push the bike itself up the hill.
I am unable to stand out-of-saddle
and pedal. I made all my most steep/long climbs on the Vado seated, Turbo, granny gear if needed. I need to mention I was even able to sing during one of my 19% Slovak climbs!