The Arcfour cypher mode (RFC 4345) uses less CPU power than most other cyphers used for ssh connections (like AES). It may be less secure, but is interesting when fastness and low ressources consumption is important. Arcfour stands for "Alleged RC4", see RC4 history (wikipedia). The Cipher::Arcfour perl module is also full of worthy details (pm file).

HPN-SSH (High Performance Enabled SSH/SCP) is a patch to enlarge openssh buffers based on the link BDP (Bandwidth Delay Product), thus removing a network throughput bottleneck:

• project page
• paper about HPN-SSH and links with high BDP
• HPN-SSH introduction by NASA's NREN