I think it really depends on the image, your guidelines sound ok for most things Misha but I do find really detailed images lose quite a lot if compressed or downsizwd too much. I agree about scrolling, especially side ways, I just feel like I can't see the image if I have to scroll a lot. I'm on dial up & only find it gets really slow around 300, depends how fast the site's moving. 200 is definitely ok.

elusive.chaos

"You need chaos in your soul to give birth to a dancing star...." (Nietzsche)