My 16gb of ram, quad core, iMac usually boots within a few seconds. After the upgrade it takes excruciatingly too long. We are talking about in the 5 - 10 minute range. Once it boots everything is fine. I did a PRAM flush from boot, but that did nothing. I am running display link for a third display, but I haven't read any of the numerous issues with display link/mavericks being related to boot times. Any help??