Running PHP and Perl in one webpage will surely degrade the performance of the webserver. For each call to a Perl-routine from PHP, the web-server will have to start a new instance of Perl. Multiply that with the number of pages that can get simultaneously accessed and the performance crawls down to a halt.
A program should be light and agile, its subroutines connected like a string of pearls. The spirit and intent of the program should be retained throughout. There should be neither too little or too much, neither needless loops nor useless variables, neither lack of structure nor overwhelming rigidity." - The Tao of Programming, 4.1 - Geoffrey James
My blog: Imperial Deltronics