Apache mpm-itk Performance

I manage a bunch of VPSs with memory ranging from 1GB to 8GB. Most of these websites are Joomla websites, and the servers must support multiple sites/users/S-FTP. I use mpm-itk almost exclusively (mostly due to it's convenience in these shared environments). However, I'm aware it isn't known for performance, so I need some advice on making it faster.

Due to the lack of documentation when I first went the way of mpm-itk, I included only one setting in the config, and that was to limit each user to 50 clients (the rest I left up to defaults):

<IfModule mpm_itk_module>
    MaxClientsVHost     50
</IfModule>

Are there any better alternatives available? Are there any settings supported in mpm-prefork or mpm-worker that are also supported in mpm-itk?

Thanks!