"Yes, not using cache at all would make everything very slow" That suggests you've not tried it. I have. I've been running with disk and memory cache disabled

"Yes, not using cache at all would make everything very slow" That suggests you've not tried it. I have. I've been running with disk and memory cache disabled in Firefox for a couple of years now on my laptop, and it's not anywhere near as slow as you think it would be. It's barely noticable at all. On my work machine I have the cache enabled, so I even have something to compare against. My laptop is usually sat on an 8Mbit Internet connection. If you're on a much slower Internet connection it would make a bigger difference, but I don't think 8Mbit is particularly fast nowadays.