What is the best background image size for web 2.0 layout?

Hello guys! I am trying to design a website that has a whole image as a background, you know!, a whole thing as the background of the site! What’s the best size that I should start my work with in the photoshop?

Example-> http://www.coolbrushdesign.com/

this photo -> http://www.coolbrushdesign.com/templates/coolbrush/images/allPage1600.jpg

Thank you!

1920×1200 is enough i think. Full HD

1920×1200 is enough i think. Full HD

Please do, or make it blend really well.

Some of the themes here stop just short of 1080p and it is sad to look at.

PS: 1920×1200 is not “Full HD”, thats 1920×1080, aka 1080P. 1920×1200 is the 16:10 variety while “Full HD” is 16:9.