For version upto P8 (provided you've got enough scrren resolution) you can just set the document window to the size (or larger) of your render.
For P8 you'll need to undock and float the document window before you can set a specific size.

If the document window is larger than specified render size, you'll get the "Production Frame" displayed to show you what will actually be in the render.

If you're rendering size is too large, you won't be able to fit the whole thing in the Render window, and you'll have to pan the image to see areas that are off-screen.