Just had the same problem updating to 1.6.1,
in modules -> top menu -> use the drop down button -> reset
How long it took me to find this ? 3 hours (plus one hour writing "PHP", "JAVASCRIPT" and "CSS" with my own blood)
hope it helps
Maybe you can improve the speed by lowering the size of your images and if you have access to ht access by specifying an expiration date for the images at least.