Even though I run a pretty fast network and vpn at home I still have the occasional hiccup running demanding applications (i.e. digikam) at home.
A few simple options can speed up X considerably. Connecting with the following parametters will enable a fast encryption cipher and also enables compression:
ssh -X -C -c blowfish-cbc,arcfour email@example.com
Of course you can make this permanent by adding the following to /etc/ssh/ssh_config (might be different on your distro):
# default line
## see man page for more info on Ciphers