DB queries fast, Apache response slow, high PHP CPU
I would suggest trying to use drupals caching to cache the page and installing a php caching system such as APC or OP cache (if using php 5.4 or higher for OP caching) and this should speed up significantly.  If you really want a performance hit then try using varnish to cache the pages.

The reason is by default apache does not do a very good job rendering pages in the sense of requests per second and can significantly increase when caching and exponentially increase using varnish caching.

So in short the following is good for performance:

PHP:
1. ) APC cache or OP caching.
2. ) Varnish caching
3. ) MYSQL caching such as memcache