Maybe interesting to know, about the forum jump menu
 

This is what our admin found out at our forums:

The forum jump menu actually uses around 50% of the BW of the whole forum. The biggest slowdowns were when bringing up the forum indexes, after a little investigation I discovered this was because the forum jump menu generates a huge amount of html. After disabling it the forums sped up noticably.

Exactly which "forum jump menu" do you refer to?

If anything, my guess is the "similar threads" section on each thread eats some CPU.