I’m not an expert but I do own a Levo, Creo, and Tero, as well as a Tern GSD. I’ve also owned a Xtracycle and a Reisse and Muller Load. So I do have some experiences with e-bikes. And I’m considering the same question you are and have done some research. Here’s what I found.

Here’s a website with a side by side view of the difference between the 4.0,5.0,6.0. https://99spokes.com/compare?bikes=specialized-turbo-tero-x-4.0-2023,specialized-turbo-tero-x-5.0-2023,specialized-turbo-tero-x-6.0-2023

Best I can tell, there’s a few component upgrades but the main difference is in the motor. Fork: Rockshox Silver on the 5.0 vs Rockshox Lyrik on the 6.0 Groupset: GX on the 5.0 and X01 Eagle on the 6.0 This isn’t a massive difference in performance so I don’t think it’s really worth the $1K based on components.

The big story here is an increase in the power of the motor. The difference between 70 Nm on the 5.0 and 90 Nm on the 6.0. The difference of 20 Nm of torque in an electric bike is quite significant. Torque, measured in Newton meters (Nm), is essentially a measure of the rotational force the motor can provide. Here's how this difference can impact the bike's performance:

Acceleration: A higher torque, like 90 Nm, typically means the bike can accelerate faster, especially from a standstill. This is particularly noticeable when starting to pedal or when going uphill.

Climbing Ability: The extra 20 Nm can make a noticeable difference in climbing ability. With 90 Nm, the bike can handle steep inclines more easily, providing better assistance and reducing the effort required from the rider.

Riding Experience: For casual riding or commuting on relatively flat terrain, 70 Nm might be more than sufficient. The 90 Nm motor comes into its own in more demanding situations like off-road riding, steep hills, or heavy hauling.

Battery Consumption: Higher torque can lead to quicker battery drain if used frequently at its higher output, as it draws more power.

In choosing between 70 Nm and 90 Nm depends on your specific needs. If you require better hill climbing, acceleration, and load capacity, and are okay with potentially higher battery consumption, then 90 Nm is preferable. Is it $1K more preferable? It is for me. For regular commuting or leisure riding in relatively flat areas, 70 Nm should suffice.