It is a well accepted fact that lots of RAM does improve performance. But does RAM speed matter in computation intensive operations? Is there a difference between 1600MHz RAM and a 2400MHz RAM in performance, everything else being equal? If so, how much?
I have googled around and came across a few links and this excellent review http://www.anandtech.com/show/6372/memory-performance-16gb-ddr31333-to-ddr32400-on-ivy-bridge-igp-with-gskill . But all of these seem to be in the context of gaming? Does it apply to programming too?
Additionally, Mechanical CAD (Solid Modeling) isn't multi-threaded in the vast majority of cases right now. There are some niches where it can help, but really we are still identifying how this might work.
For CAD, you want a very fast CPU and fast being single thread performance maximized, and then fast and a lot of RAM.
The order depends. Small, but complicated data sets favor speed over size.
Larger ones demand both.
On the software I work with, that big of a jump in RAM speed, coupled with a good CPU and cache can reach 30 percent faster update / build times. When those are seconds, nobody cares. When they are an hour, yeah. Big deal.
CAD is also compute intensive, meaning it's a great system stress case.