I looked at Zuzu's kitty photo on cubits, the actual photo measured 9 and 1/4 inches wide by 7 inches deep. The photo here opened slowly first time, it's a little frustrating, but the second time it opened straight away. It measured 9 and 1/8 inces wide, 6 and 3/4 inches deep so was only a little smaller. I tried this last night, some opened quickly the second time but others didn't then on another attempt they did. The first opening is the one which matters as most people are not going to open a photo twice just to get it to load more quickly.
My monitor is a widescreen 19" (diagonal), I always have the browser window full width which horizontally is 16" but it's only about 10" deep. I wonder if that makes a difference too. I have IE but it's a BT Yahoo version. I also have a new high spec computer which should be super fast, maybe it's time to clear my cookies.