PHP pages have a reputation of being more difficult (or at least different) to SEO than static HTML pages. Here is an overview of the major issues encountered when trying to optimize PHP script for search engines. While this focuses on PHP much of it is still relevant to SEO ing dynamic pages in general.
While page size does affect load time, spiders run on servers connected to high bandwidth networks, so download time is less important than the latency of the PHP script execution time. If a search engine spider follows a link on a site and is forced to wait too long for the server to process the PHP code behind that page, it may label your page as unresponsive.
The biggest delays in a PHP script typically are the database and loop code. Avoid making SELECT * calls, instead explicitly name all the columns you want to retrieve, and if you are using MySQL, test your queries using the EXPLAIN statement. To optimize loops consider using duplicated code instead of loops that don’t repeat very many times, also use as many static values, such as count($array) values inside the loop as you can, generating their values before the loop once.
Use of Compile Cache
The execution times can be improved by implementing compile caches like Turk MMCache (https://turck-mmcache.sourceforge.net) or APC as a php module. Though I do agree, that these would not be sufficient where contents are changing dynamically or across time.