Compression is a funny thing. You cannot accurately predict the exact compression ratio without knowing what the files are and the algorithms being used. Some files, like MP3s are already compressed. Text files compress a lot, JPG files do not. By using the /Compress Maximum switch in the ImageX command line will put a lot of work on the capturing of the image, and less on the transfer of that image.
For this reason, I make sure that I am absolutely satisfied with the image that I am about to make. We are going to have an upfront cost of more time to create the image, but we will make it up if this image is going to be sent across the network many times.
I decided to do an experiment with a new Windows 7 Home Premium edition client that I just picked up at the store today. I only ran the basic configuration and loaded the Anti-virus software. Only imaging the C: drive and using the default compression, the image file size was 20,949,078 KB. The size of the image file after making a new image with the maximum compression option set was 10,263,386 KB. That was a reduction of 10,685,692 KB or 51%. That can be a huge savings in network bandwidth.
For a Thick Image (one that contains software as well as an OS), you may have to start the image capture and come back in the morning. But again, we are making an investment now, to enjoy a greater return on that invest later.