I'm new here (and new to actively using support forums in general), but i have similar issue, i think.
I'm using the trial license for a month now, started with version 6.9.0 on a relatively old and low performance system running a G3240 Pentium processor and 8GiB DDR3.
I'm using the system mainly as a media server using 3 2TB WD Red drives (1 parity) and no cache. as part of my evaluation process i've tested the transfer speech of the SMB shares and compared to my old WHS V1 machine that i intend to replace. I was getting relatively low transfer speeds that went even lower after a few GB of the file were transferred and CPU load was reaching 100%, after searching the forums i've changed the "Tunable (md_write_method):" to "reconstruct write" which helped a little but still i will get the high cpu load and the drop in transfer speed after a few GB.
reading further in the forum i found a post that suggested rolling back to 6.8.3, i did, and have a steady ~90-110 MB/sec transfer speed most of the time and CPU load is lower too.
I've installed Fix Common Problems plugin which warns me now that i should update to the latest version, which is probably a good idea but i don't want to lose the smb performance.
As I'm evaluating still and jumping back and forth between builds is pretty painless (so far) i think i'll upgrade and test the speed again. anyone here familiar with the issue?
i apologize in advance for maybe stealing this thread