It's quite obvious that if you opt for Dual Quad Configuration, the performance of the server will be higher compared to single quad. However, why not study your requirements and only then select the option of the processor as there will be difference in the pricing of both.
Keep in mind your licensing cost go up with a Dual CPU. Also make sure the MSSQL version your using can address the Dual CPU's.
Very important point to keep in mind with respect to your budgets as Microsoft product licenses are available on 'per CPU' basis. In addition to dual CPU license for SQL Server, you will also need to purchase dual CPU license for base OS. Hence, if your requirements are not much demanding, you can opt for Single Quad to reduce your licensing cost otherwise, you can opt for Dual Quad where license costs will double. For your reference, below are max number of CPU's supported by each editions of MS SQL 2005:
Enterprise: OS Max.
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The database will be used for a mid size e-commerce site with two front end web servers running custom .net application with load balancer.
We will be running MS SQL 2005 standard so it will support dual quad core.
The site traffic will be average 60k unique visitor, 700k page views and 3k orders per day.
As for the budget, I think we can negotiate down to be less then $800/ moth so it’s not a huge issue (we will be leasing).
The hosting company originally quoted us single quad core for the DB server but I opt to increase to dual quad core.
I understand there will be performance gain but I like to know how much since I can’t seem to find any bench mark data compare the two different setups for SQL.
We run a MUCH larger setup on lesser hardware. A config that can easily handle that is:
2 x Web servers 2GB ram each - stop unnecessary services make it an IIS only server.
1 x DB server single Quad 4-8gb ram. - stop unnecessary services make it a Tuned SQL server (trans and db files on separate drives, let sql optimize itself across all processors)
Dual quad's for DB will be gross overkill for that server. The reason there is no benchmark is because it is simultaneously easy and also quite difficult to do what you are asking.
Difficulty: Depending on the way your app is coded, caching, disk type and the strucutre of your DB including indexes, you will see different results.
Ease: Well you have 4 additional cores which is double so you have double the processing power. The question is if your app needs it or can utilize it. If you are multithreaded you will use the available cores but you will see a ton of idle / almost idle cores all the time.
With the dual processor setup you just doubled your licensing costs so don't do it until you need it. With the volume you quoted you really don't need it. Instead invest in fast drives.