As Ram speed generally shows farily marginal gains even in benchmarks i would presume the same is true for SolidWorks although i haven't seen any tests of higher speed ram.
Generally the money is best invested in CPU the fastest quad core you can afford is generally best for just solidworks, you may consider more cores if using simulation or rendering.
Graphics card is still important but not if we are talking about rebuild speed. There are some good graphics card comparisions on the forum and media lately. https://forum.solidworks.com/thread/64436 and http://develop3d.com/hardware/graphics-cards-for-cad-ptc-creo-2.0-solidworks-2013
Thank you for your answer Alan.
I've got a small comparison on the memory speeds:
Memory score using Solidworks benchmark 1600MHz memory: 70 seconds
Memory score using Solidworks benchmark 1866MHz memory: 53.8 seconds
Though this comparison has been made with different processors, videocards and SSD.
You can see the systems <here> (Workstation Guido, Frank and Arno)
The fastest system (Guido) runs at 4500MHz.
Regarding the brand of videocards, i'm pleased with the AMD (not ATI) series.
Drivers seem very stable, in the beginning they had a glitch about once a month.
Using the latest drivers now and there are no problems anymore.
Looking at bang for buck the AMD cards are cheaper for the same performance.
Interesting, i've always felt that faster memory might be useful when swapping alot of data between memory for instance with Simulation the mesh and result files are quite large, but never been able to do testing with like for like systems either. It would be interesting if anyone has?
edit atleast some testing here, http://techreport.com/review/20377/exploring-the-impact-of-memory-speed-on-sandy-bridge-performance/4
not solidworks but mentions benifits for a fluid simulation package. Otherwise it is more hit and miss with real world applications