Unfortunately SFTP isn't a good replacement when speed is a concern, anything running over OpenSSH will have its bandwidth limited by the fixed window size. I long for the day when HPN-SSH replaces OpenSSH everywhere.
Most of our transfers are limited by our backbone, but because we chunk files we're able to do multiple concurrent transfers and max out traffic as best we can. We mostly have 10g links, but anything over that tends to get into serious diminishing returns in value/performance.