Something to keep in mind is that 6.0 is out of date and you may want to wait until CentOS 6.1 (or the updates to it) are available.
At the end of November, Eivind Uggedal posted a comparison of various VPS hosting providers. In particular Linode, Slicehost, Prgmr, Rackspace and Amazon are compared using various performance tests. 64-bit and 32-bit performance comparisions are also discussed.
You can find the comparison at http://journal.uggedal.com/vps-performance-comparison.