If you are developing the software then you should use the lowest performance machine that your customers are likely to use.
If you are testing the software because you are the customer then you should look at web sites that specialize in testing hardware. Here are a few really good ones.
That's about half of my bookmark list for hardware reviews. Look for articles with a name generally like "CPU Roundup". The last time that I did a lot of research on CPUs it looked like the AMD FX series was your best bang for your buck.
In general I would recommend getting the higher on chip memory. Some dual core chips have separate cache for each core. Sweet. Single core CPUs also benefit from a lot of L2 cache.
If you get an Opteron then you want to think ahead. You may want to eventually purchase more than one dual core CPU for the computer. If that is the case then you will need to purchase the correct Opteron series. The series 200 will allow you to have 2 dual core CPUs on the main board. The series 400 will allow you to have up to 4 dual core Opterons on the main board, and the series 800 will allow you to have up to 8 Opteron dual core CPUs on the main board. Then they also have the high efficiency series (HE). These generally use about half of the electric power of the regular Opteron CPUs.
Don't neglect other things like RAM, disks, main board clock speed, bus clock speed and width. You will probably benefit by having at least 1 GB of RAM, a PCI-Express bus, and second generation SATA controllers and disks.
When it comes to motherboards I have never looked at the AMD approved list. Over time and purchasing a lot of motherboards I have become fond of motherboards with Nvidia chips. The VIA chipsets are ok but I think that the Nvidia chips provide higher performance. This is particularly true if you use an Nvidia graphic card. IMO, of course. :-) I'm sure that some other people would do exactly the opposite based on their own experience.
I hope this helps.
Last edited by stress_junkie; 08-15-2006 at 12:44 PM.