Once again, CMS's like WP, Joomla, Drupal, etc. require an excessive amount of CPU time for every request (unless you've done a lot of cacheing) so I'd recommend "specialty" accounts which cater to these CMS's with limited accounts per server and a greater percentage of CPU time.
Fortunately, I'm only aware of a single host which provides this type of account: http://www.webhostingbuzz.com/wordpress-hosting.php (for WP, see the bottom of the page at http://www.webhostingbuzz.com/ for Joomla, Magento, Drupal and E-Commerce). Note that I said "Fortunately" — that's because I've found WHB to be an outstanding host, i.e., good prices, up-to-date hardware and software and an incredible support staff. With servers in both the US and UK (http://webhostingbuzz.co.uk), you can target your visitors, too!