Get the 5820k, much more useful for multi threaded workloads in solidworks, though it depends on how intense your work is. If it's hobby type work making random crap you'll find that solidworks isn't even that intensive. If on the other hand if you are creating large assemblies and working with a lot of polys in applications such as automotive, aerospace etc you will probably want even more threads from something like a xeon.
Whatever the application, the 5820k is by far the better processor and is only at such a good price because its falling into irrelevancy - making it an brilliant deal.
Also, if you are going for large part assemblies then consider a lot of RAM