This article describes FTP settings that can improve upload and download speed.
Select burger menu > Global Settings > FTP tab. See the help file for details.
Also, threaded scanning can greatly reduce the time it takes to scan an FTP server. To use this, modify your profile, go to the FTP -> Advanced settings page and increase the Scan Threads value. See the help file for details and limitations.
With SE/Pro, performance can be significantly improved by using multiple worker threads. Using worker threads, SyncBack uploads or downloads multiple files at the same time (with each upload/download using one thread). To use worker threads, Modify your profile > FTP > Advanced settings page and increase the Worker Threads value.