I do not know beacuse I never had the Zoom browser; however, this is just a guess...perhaps it could be lack of RAM for your computer? Because your images (assuming they are high resolution or raw) are very large in space, therefore using your Ram memory to produce your images on screen. Now I don't know what kind of Computer/Hardware you have, but that is my idea behind this. If that isn't the case, then you may want to contact Canon technical support via email and see what their stance on the software being slow is.
This new software is junk. The old zoombrowser would load new images in seconds and the new crap takes 30-60 minutes. I have a new top fo the line fastest HP workstation you can buy. I gave up and just use Windows explorer with thumbnails.
Dear Canon, Your software is crap.
Also just downloading the images is 10 times more work. Before I plugged in camera and it did it all, removes images from camera without interaction. Unplug camera.
Now I have to OK the "auto" download, then OK when done, then OK to close it. *Removed per forum guidelines: http://forums.usa.canon.com/t5/Forum-Info/Forum-Guidelines/m-p/15
This is my last Canon, you SUCK!