If you want to sudo, but then allow X Forwarding over SSH, I've found the easiest way is to copy the xauth information from the logged in user to root.
For example:
- Enable X-11 Forwarding in your client
- Log in as your normal user
- Type `echo $DISPLAY` to get the associated display
- Type `xauth list` find the display number which corresponds with what you found in #3 and copy it
- Sudo to root
- Type `xauth add <paste in what you copied from #4>`
- Now you can execute commands as root and will be able to use the X11 Forwarding connection established by the parent user