Adserver programming with php

Hi there, I am thinking about creating a kind of adserver which is customized for my needs. As I would be most confident in doing this with php, I am asking myself if this is the right choice or if it would be wiser to take a C++ aproach for example to get a higher performance just in case the site grows fast. Do you guys think that a php build webserver would be able to scale and perform well enough for serving millions of adimpressions daily? Thank you for any advice, Merlin