Good morning. I'm spanish, my conoucements of the english language is very small, I'm sorry in the errors.
This is the problem: I installed the OpenWRT in the router Archer C6 V2. Function very well, but the space of installation for the new applications is very small. After install de OpenWRT, the free space in the disk, is 212 KiB. I Upgraded the system in the router to the last version.
The "temporary space" is a virtual disk in RAM. Any files stored there are lost on a power cut or reboot.
The only difference between EU and US version seems to be the size of the flash chip. So you could potentially convert yours to 16MB flash and run US firmware. The US version should be supported into the future.