I know this is an old thread, but the above changes did not help me in my case. What I found was the ordering of the ciphers played an important part in speed for SFTP from the vendor we were connecting to. At most I could get was 5.5Mb~ but after the below changes we were up near the 25.5Mb~ range. I would suggest adding a mention to ordering the supported ciphers to the FAQ.
Raw settings for my session options were changed from
Came across this article that helped explain the impact of the ciphers used on SFTP speeds which helped us to improve the transfer speed.