how do I determine the source resolution coming out of my graphics card?

my Quadro fx 3450 says it has support for ultra high-resolution panels up to 3840x2400, and Single Link DVI-I output drives digital displays at resolutions up to 1920 x 1200 @ 75Hz.

If I'm editing 1920 x 1080 video, is that the raster display size the card will be sending to the monitors?

thnx

no , the size sent to the monitor will be the one choosen in display adapter settings.
over 1920 you need a dual-link DVI, and over 2560 you probably need a dual dual-link dvi.
if your card has different output (hdmi, component) it could give you a video signal that is not at computer standard (like 1920x1080 for HD ) but there is probably a control panel for that too.

So yes, if you got a 30" screen set at 2560x1600, it could play full screen HD (1920x1600) rescaled.