What kind of work is it? 2D or 3D? Office work or Mobile?
Perhaps i have a few suggestions for you.
Dolf Koppenol
Hello Cadman, here are the specs for a workstation for AutoCAD and Revit. (not Inventor!)
processor: Xeon E5-1620 v2 Quad Core 3.7Ghz <= best speed
Memory at least 16 GB better 32 GB
Video Card Nvidea K4000 (3GB)
SSD 265 GB or better (no Hard Drive but Solid State)
I have not find a complete Workstation by Dell, you have to customize (Dell Precision T1700 Mini Tower)
Look for a HP on the word 'WM679ET#ABB' just as a example.
If you work with large drawings/models you have need for a fast network (1Gb/s) and a fileserver.
For Revit there is a kind of server called Revit server/Accelerator.
See:Revit-server
There is no thing as a cadworkstaion, without network, fileserver plotters etc.
we purchased Boxx computers... over-clocked processor, liquid cooled, solid state drive, etc.
I did extensive performance testing before our purchase... and these computers out did the speed improvements we got when we jumped from 32 to 64 bit back a couple years ago. We got all new for our whole CAD detailing group! We had a few of them upfront that produced blue screens... but their support was very quick on the spot and now we are all good.