I looked for some benchmarks, and I would know if I'm right on: - Dual Opteron 246 have aproximately the same performance of a Dual Xeon 3Gh (Opteron a little better) - Opteron system equal or cheeper than Xeon system.
In terms of general database performance, top of the line dual opteron will perform roughly the same as top of the line dual xeon. Assuming you just run in 32-bit mode. Throw in 64-bit mode, NUMA, etc, all bets are off.
In terms of Postgres database performance, Opteron *may* be the better CPU for this app but there's not enough data points yet. Here's a recent review at Anandtech showing Opteron 150 (2.4ghz) versus 64-bit Prescott 3.6hgz with some very simple MySQL and Postgres benchmarks:
http://www.anandtech.com/linux/showdoc.aspx?i=2163&p=2
What is a slight lead in MySQL becomes a blowout in Postgres. Of course, this is just the 1MB cache model. I'm sure if you went with the 2MB or 4MB models, the Xeons would come up much closer.
The really good sign in the above numbers though is that somebody finally included Postgres in their benchmark suite. :) We may be seeing more and more data points to evaluate hardware for Postgres in the near future.
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