The actual settings are optimal for any server.
But, if you want to change the number of threads/posts displayed on each page, do the code change listed below.
FILE: forumdisplay.txt and showthread.txt
FIND:
Replace the numeric value with the one that suits best for your forum.
The bigger it is the faster the crawers will index your pages.
Do not go over value 400, just to make sure you give a break to your server also.