If you don’t need more than 16 GB of ram the mid-tier might have slightly better battery life than the top-tier, however that difference is likely very small. (More ram can consume more power, although if you are running out of ram the system will start paging which consumes even more power)
Both the top and mid tier should have significantly better battery life than the low tier. This is because the low tier has a smaller battery (55 Wh vs 61 Wh) and uses a weaker CPU.
A common misconception is that more powerful CPUs inherently consume more battery. But that isn’t automatically the case.
The 7640U is the same CPU design as the 7840U, however the 7640U has 2 CPU cores and 4 GPU cores permanently deactivated (either due to being defective or just cause AMD needed to meet demand for 7640U so they crippled some 7840U chips).
Ryzen processors tend to be pretty good at automatically putting most of the cores to sleep under low load (where they consume negligible power). So under low load the 7840U deactivates its extra unnecessary capabilities and behaves exactly like the 7640U.
Under heavy load both CPUs will consume 28w of power (what Framework’s cooling system is rated to handle), however the 7840U has more cores each operating at lower power (same total power as the 7640U). More cores each at lower power results in better performance than fewer cores each at higher power.
So both CPUs will consume the same amount of power under both light and heavy loads, however the greater performance of the 7840U will allow it to complete heavy loads quicker and overall consume less power.
IMO all but the base model Intel models are way overpriced.
Framework offers 3 models of Intel CPU: 1340P, 1360P, and 1370P.
The 1340P and the 7640U are competing CPUs and priced the same amount (in the Framework Laptop).
However the 1360P and 1370P are where AMD absolutely destroys Intel in value. The 7840U is competitive in price with the 1360P but competitive in performance with the much more expensive 1370P.
IMO the 1360P is such a small improvement over the 1340P that it just shouldn’t exist (and the 1370P should be priced at the price the 1360P is currently at).
The 1370P is just overpriced IMO. One of the selling points of the 1370P is that it supports Intel vPro Enterprise. vPro Enterprise is a suite of tools that allow a company to remotely manage large fleets of computers. It doesn’t matter to 99% of end users, however to the massive corporations buying thousands of laptops it is a feature they are willing to pay a premium for, so Intel prices vPro Enterprise capable CPUs at a premium.
The AMD CPUs tend to be more efficient and have much more powerful iGPUs.
Part of the efficiency comes from the lithography (manufacturing process). AMD is using a TSMC 4 nm process (the number loosely corresponds to the size of the transistors) whereas Intel is using their own process (which they used to call 10 nm but now call Intel 7 because they claim it is competitive with TSMC 7 nm).
So AMD is using a more modern and efficient manufacturing process, which helps a lot with efficiency.
Furthermore AMD’s cores seem to be generally better at providing high performance (at high power consumption) which under heavy load but efficiently dropping down to low power when high performance isn’t needed. Intel on the other hand has resorted to having some cores optimized specifically for high performance/high power and other cores optimized specifically for low power.