Based on a previous blog, which has been rendered obsolete as I realised lately, here comes the new revision:
To increase the transfer speed between you Mac and your SMB NAS, you will have to change the default configuration of you Mac.
[Update] I figured out some new configurations and updated this post.
Change the file at /etc/nsmb.conf:
[default]
dir_cache_off=yes
signing_required=no
notify_off=yes
protocol_vers_map=4
You may have to reboot your Mac, since the SMB shares appear a bit more persistent than before.