I bought a retina iMac but due to being dumb I only got the 256gb SSD version. Now I don't want to dedicate half of that to Windows. My iMac has USB 3, thunderbolt 2 and an external storage card. Is there any external storage that I can buy that's between $100 and $200 that is fast enough that running Windows from wont be excruciatingly slow? edit: I have this http://usbflashspeed.com/device/73779 but really don't know if it's too slow.