After comparing both Bananian and Armbian, I noticed Bananian follows the rules defined on the site above (linux-sunxi.org), for the type of governor and some "ondemand" settings. This made the web download pratically the same as Bananian's, at 35.5MB/s.
Still, Samba shares were the same :-( So, I tried to just copy the smb.conf file from Bananian to Armbian, maintaining my defined shares and finally things fell into place! :-) I didn't actually check what was the difference except there are no special "performance" or "tuning" settings there, like socket options, or aio read/write size, etc.
I still think performance was better on my old, now lost, BanaNAS installation. But, it's acceptable.
Thanks for your tips!