Regarding the 4GB vs 2GB and battery life.
Depending on the storage device you use, having the extra 2GB act as cache (Linux does this automatically) can help reduce power usage by having the storage devices stay inactive and the CPU can return data immediately rather than run all the code required to read from the storage device and "pollute" the CPU caches which reduces efficiency.
It depends on how much power is required to read from the storage device (CPU, DMA, Storage device workload), how much is avoided, what the consumption difference is between 2GB and 4GB, and how many I/O reads are saved.
Also, keeping well-behaved-when-inactive programs (eg: NOT browsers) in memory, rather than unload/reload them repetitively, can save battery life because of all the CPU work required to load and dynamically link a program.
Citation:
https://www.wired.com/2016/03/closing-apps-save-battery-makes-things-worse/
Additionally, the extra 2GB can be used to mount /tmp from tmpfs to use RAM instead and spare the flash storage. Which I bet is how the Pyra OS will be configured by default.
You can do the same with your browser cache but this means the browser cache will be lost on every reboot (which might be what someone wants anyway)
All of these can offset the higher power drain of the extra RAM.
BTW, anyone knows what the exact mWh difference is between the actual 2GB and 4GB setups when idle and working? If that info was shared I missed it.