I am in the market for an iMac. I want to have an SSD for the benefits I have read about. I know I don't want to attempt to do an SSD upgrade myself and chance damaging a new iMac and voiding my warranty. Adding an SSD when ordering adds more time before your computer ships. Is there a good option to add a thunderbolt SSD, or is it better to just go ahead and order the internal SSD when ordering?