Slow FTPS (Explicit)

As part of the new requirements of PCI compliance, we have to run FTP over SSL, now I've switched over Smarth FTP to FTPS (Explicit) in the setting for all of my sites which is simple enough but I've noticed a lot of lag when the files are sent / recived they often stop and I have to manually process them to get them to upload. I've reset the the retry time to 6 sec rather than the default 40sec but it still takes alot longer than I expected is this normal or can I set up Smart FTP to process the file quicker ? Any help would be great.

Cheers Nick.