I've got the 15" rMBP at home and it's blazing fast. Recently, I upgraded my work machine (2.7GHz i5) to 12GB and an OWC 240GB solid state drive. In my experience, you can't get more bang for the buck than throwing an SSD into your computer if it will take one. OWC doesn't show any installation videos for the new iMacs though I know you can get up to a 768GB SSD in the high-end product. SSDs are a game changer!