How important is CPU cache?

Hey guys,

I'm currently looking at getting a Win8 ultrabook with Intel's ULV processors.... I was hoping you could help me understand the differences I'll experience while using the device between the i5 and the i7 (clocked 200 MHz higher with 4 MB cache instead of 3). This will be my only computer and although it's primary use will be for just watching videos, listening to music and surfing the web, I will also use 3D modelling programs such as AutoCAD and SolidWorks from time to time. Where will I notice the biggest differences and is it worth a $200 upgrade? Thanks.