Looking at the 13" it has an added benefit I see which is the SD card slot. I am wondering if the speed of this (given a fast card of course) can act as a second hard drive and thereby compensate for the relatively small 128Gig SSD? I know it is way slower regardless than a 256 SSD but significantly cheaper too... I was thinking data files, media etc. Or would this be too slow compared to like an external USB based HD? I would think it would be faster but I don't know. Insights?