Q:

WordPress MySQL Performance

I have a website (www.americanbankingnews.com) that gets 40,000-50,000 page views today.  It's currently sitting on a dedicated quad-core Xeon server with 8GB of ram.  The site is powered by WordPress and MySQL (sitting on the same server) and I'm currently using W3 Total Cache for page and MySQL query Caching. 
Unfortunately, that doesn't seem to be enough.  During peak traffic times, my servers are getting a few HTTP 500 errors and pages that aren't cached load slowly. 
I'm currently not using Xcache or any other PHP cache/acceleration tools.  
Are there additional steps that I should take to try to optimize MySQL and PHP performance?  Or should I fork over for an additional server.  Specifically, I'd be interested in additional suggestions to improve MySQL performance and whether or not tools like xcache might help in this situation. 

A:

Before concerning yourself with the machine, have you done a thorough audit of your WordPress install's plugins, templates, etc.  yet? 
I have a client in the 30-40k/day range on a shared host, with a large portion of the site requiring authentication to read(so we can't quite do full-on "static" SuperCaching), and they've yet to have any significant performance complaints.  
If you're chewing through a dedicated machine with only another ~10k visits, there might be more going on than just an underpowered server.