I have done some load testing on miniBB and notice that the function parseTpl, that reads HTML template files and paint the page is very heavy. Assuming that the filesystem caching is setup correctly to avoid i/o waits on reading template files, I suspect the time is spent in string manipulation in that function. Under the covers PHP use RegExp for all string manipulations. It would be better to use RegExp instead in the parseTpl function directly to avoid slowdowns.

Any thoughts? code snippets on how to adjust the parseTpl function to use RegExp instead and be able to do the same?

Could you give an exact examples of your testing? Statistics, screenshots?.. Why do you think this function slows the performance? In comparision to what did you this testing? This function was implemented exactly because regular expression functions are much SLOWER than general string parsing functions.