ctcadman :
I'm looking Dell T7400 Workstation Dual 2.66 GHz E5430 QC Xeon processors. How much faster is dual than a single CPU? Would be up in the range of and of the I series processors. If I wanted to upgrade the cpu's what would you put in? This is being used for 3D cad/inventor.
It sounds like you are looking at possibly buying a machine but have not done so yet. I would personally not buy this machine unless you can get it for nearly free. The E5430s were decent processors in their day but they are five years old. Two E5430s will at best perform like a decent single modern quad-core Core i5 or a six-core AMD FX and at worst slower than any of them since the E5430 does not have any form of Turbo Boost and those other processors do. One E5430 would perform like a Core i3 at best. There is some limited upgrade ability for that motherboard. The fastest CPU that will definitely work is the 3.00 GHz quad-core E5472, which will be only about 10% faster than the E5430. I would skip the upgrade. The biggest issue with this machine is the chipset that it uses. The i5400 chipset this machine has uses FB-DIMM memory which runs very hot and is extremely expensive to buy, particularly the DDR2-800 FB-DIMMs the T7400 uses. This memory also has very high latency and kills the performance of the CPUs. The shared frontside bus architecture of the i5400 adversely affects application scaling when adding more CPU cores.
So in short, look at a modern machine and leave this one for the history books unless it's nearly free. If it is nearly free, use it as is and don't upgrade anything because it will be very expensive and not give you much of an increase in performance.