Based on my own experience (dial up) it's very slow taking between 13-22 seconds to load a page after clicking a thread title. Occasionally after 30 seconds I hit the refresh button as it's dificult to tell whether it's frozen or is still downloading. I've clocked it downloading half a million bytes to login and go to a single thread.
It's probably due to the popularity of the site with many accesses at the same time.
What you're saying is a bit worrying for me though as I was considering going for broadband mainly for this site. I don't think I'll bother now.