As long as you don't have a monitor running removing the card saves virtually nothing.
Do you have a source for that? In my world, I don't see how turning the monitor off (or rather having the OS put the monitor to standby/off/whatever), would do anything to lower the power usage. Anything still drawing to the screen (a screen saver, a game or something) would still be active with the monitor in standby/off so how would that lower the power used? Or nowadays when you have folding@home or similar using the GPU for processing, it would definitely still use a lot of power?