I was having major issues with slow/non responsive pages a month or so ago.

Two weeks ago I set up a brand new mac book from scratch (no time machine restore). Evidently, I had some software not playing nice with macOS 10.13.3. I only bring this up as I had the same issues with slow/non responsive pages with the new install of Safari. Last week I change my settings to "Disable Infinite Scroll" and this site has worked like a champ since.

One other data point - before the change, Safari would crash intermittently when reading active threads. I would get a memory error message indicating saying something to the effect that the page got too large for memory (don't remember exact message).