From what I’ve seen, Both models are supported with the NSS version. You can visit this page for more info.
Fixing the flash quirk for the R7800 appears relatively simple enough by following the instructions in it’s device page
You can review the C2600 device page here
EDIT: I misread the R7800. The quirk is if you’re compiling your own image and flashing the kernel. I’d suppose if you use any images found in the OpenWRT site/forum, you’ll be fine.