I've used parsyncfp2 which I think is just another implementation of the same thing and I've definitely seen 2x-3x throughput improvement when transferring over

I've used parsyncfp2 which I think is just another implementation of the same thing and I've definitely seen 2x-3x throughput improvement when transferring over large distances. As you mentioned it definitely depends on how the ISP handles traffic. I have yet to try but I've heard good things about hpn-ssh as well.