Help me look at the numbers :)

So, I'm looking at getting a new ultrabook and need to decide on what hardware configuration I need. I've highlighted the differences between the base i5 and the upgradeable i7.... but my extent of understanding these numbers is that bigger means faster which is better... pathetic I know. I'm not overly concerned with graphics, the integrated Intel HD 4000 will suit my needs fine I don't need to game on it. But I do use 3D modelling programs like AutoCAD and SolidWorks. Is the i7 worth the extra cost and will it help with just everyday multitasking?