Here's the command I found to set the default gnome-terminal height:
gconftool-2 /desktop/gnome/applications/terminal/exec --type string -s 'gnome-terminal --geometry=85x40'
Now when I hit "meta-t" I get the size gnome-terminal that I like.
Oh, to get "meta-t" to work, you might want to set this as well:
gconftool-2 /apps/metacity/global_keybindings/run_command_terminal --type string -s '<Mod4>t'