Native OpenSSH performance seems quite good these days- are you certain this is still necessary? Either the SSH client and server I used had this patch, or the windowing code in SSH was removed/modified.
The main problem is that the internal buffer size for OpenSSH is limited to 2MB (actually it's closer to 1.25MB in real world terms). This is pretty good for a lot of home users. However, HPN-SSH was written for the HPC communuity where we have have BDPs of well more than that (8MB is not uncommon). So if you have a BDP of more than 2MB HPN-SSH is still going to be a win for you.