Hey tobyaxis, already off topic on the second post, and this time it's your doing

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I used to work at an authorized HP Computer repair store. Almost all of the problems (9 out of 10 or better) were caused by adware/spyware, viruses or idiot operators (a.k.a. I/O errors or ID-10-T errors). Except for the occasional hard drive or case/power supply/CPU cooling fan failures almost all other problems were due to catastrophic failures resulting from an unexpected electrical event (ie. a thunderstorm).
No matter what model you select, make sure that you read the warranty. This is especially important if this is a production, money earning
CAD/
CAM Work Station rather than a "for hobby use" machine. All of HP's Work Stations seem to have 3/3/3 years warranty (parts/labor/onsite). If next business day repair is not included in the warranty, see if you can purchase a warranty upgrade unless you have a backup work station.
The other important item to consider is choosing a graphics card. Make sure that if the graphics card is included your software package supports it. Vice versa, find out what graphics card(s) your software package supports and make sure that the graphics card manufacturer will provide support for that card in the workstation you choose (double check graphics card speed, slot type, and voltage requirements).
I hope that helps. It's always fun picking out a new computer and waiting for the UPS/FEDEX truck to deliver it.