I currently have 2 1U rack servers, one running IIS the other MySQL. I'm replacing the database server because the hardware is old. The new server I purchases is also faster than my web server though, So I'm trying to decide which server should take each role.
My Current Web server is a Dell R200 with an Intel XEON X3220 and 4GB Ram. My new server I bought is a Dell Poweredge 1950 with Dual Intel XEON X5460 and 16GB Ram.
I also bought an Intel SSD for use with whichever server becomes the dedicated database server. Both servers currently have 10k SAS drives.
The X3220 CPU Passmark score is 3,000 the X5460 CPU Passmark score is 10,000
It seems to me that PHP uses a lot more CPU than MySQL. I host 30+ sites on IIS all of which are PHP and a few run on Drupal. It seems like it might be an easy choice but its a huge amount of work to transfer everything from the one server to the other. And maybe i'm not correct in my thinking and MySQL can really benefit from the faster CPU.