What causes slow SFTP up/download speeds

Are SFTP up/download speeds something that's in the control of the hosting company? Can they throttle SSH traffic, regardless of the port?

I just signed up with a new hosting company. We'll call them Slow SFTP, Inc. I have another server with Fast SFTP, Inc. Both are in Dallas and both are in different data centers.

I noticed my SSH client (PuTTY) lagging when connecting to Slow SFTP, Inc., so I decided to run some tests from both companies. I ran several tests over several hours. I also changed sshd ports just to make sure traffic wasn't being throttled based on the port. It made no difference.

     | Slow SFTP, Inc. | Fast SFTP, Inc.
-----------------------------------------
UP   |    744 KB/s     |     352 KB/s
DOWN |    150 KB/s     |   1,723 KB/s

I find it strange that the download speed from Slow SFTP, Inc. is so much slower than the upload speed.

Note: These are 1:1 comparisons. Identical setups on both servers. No firewalls. Vanilla Debian 7/sshd installs.