I've run Solidworks 2013 in Parallels on my 1.3 GHz rMB quite a bit and haven't had any issues at all. I agree with
azzawaba -- don't use this as your main CAD machine -- but it's very usable for light CAD work on the go.
You do need to do some registry editing to get things running smoothly, though. If you don't, Solidworks may assume your video card can't do 3D and will use software OpenGL, which is really slow on just about any machine. Software OpenGL is to blame if you go to select something and it takes seconds (or even minutes) to highlighting all of the edges of the part in orange.
Assuming you're on Windows 7, enter "regedit" in the Start Menu's Search bar and hit enter. Then navigate to "HKEY_CURRENT_USER\Software\SolidWorks\SolidWorks 2013\Performance\Graphics\Hardware\" and go to Edit > New > Key to create a new registry key. Name the key "Parallels and Intel Inc." and then go to Edit > New > DWORD (32-bit) Value and name the new value "Workarounds". Finally, double click on "Workarounds" and enter the value data "4000480" (leave Base as Hexadecimal). Start up Solidworks, and make sure that "Use software OpenGL" is unchecked in Tools > Options > Performance.
Also, turn off Real View, part shadows, and reduce "Level of Detail" in Tools > Options > Performance.
Edit: source for the registry hack is this Parallels forum posting
https://forum.parallels.com/threads/opengl.114508/