I don't know the answer to your questions about performance, but what you're describing sounds so severe. Why is nobody else reporting this as it seems to me to be a real stopper for using any of the linux distro's?

Not having done so myself, but if you go through the standard installation procedures and end up with a slow as molasses system that you describe what good would it be to anyone? I'll be installing the lates Debian Woody soon myself and I'll let you know, honestly, the kind of a performer that I end up with. The only other linux that I've used is Red Hat 6.2 and it has performed really well.