I did the exact thing I described to you for these images. I rendered the scene outside the window first because the DOF and ray trace through the window glass was crushing Carrara's render times. So, a quick 'background' render which was in focus (just a few minutes), then blur in photoshop, add back into the scene as a background image (turned off all the actually CG background stuff) and then could experiment with textures on the windows and bottles with render times that were waaaaaaaay less than what I was experiencing earlier.