Hi everyone

well, i know that i am in Australia and therefor the prices will be completely different, BUT i can say that i have tried all the gearboxes that you have mentioned.
Yes max, the 5:1 low profile in my heavy KV-2 are underpowered

The Taigen 4:1 black metal are superior for low speed and torque.(metal Sturmtiger)
The standard HL nylon are ok if you replace the ratchet gear wheel with a metal one.(HL standard M4)
And Albinator, the red gearboxes that you found, these are HL Ultimate gearboxes. They have thicker side walls, metal gears with bearings, and an improved motor, but they are 3:1 ratio. A good solid gearbox in a fast moving tank -T34.
So, i hope this helps. Its just a question of money and what you are fitting it in.

Cheers
Afrikakorps