Sorry if this has been done to death, but...I want to order a new iMac to replace my mid-2010 21.5 iMac, and I'm torn about the fusion drive thing. I actually placed an order for a refurb 21.5 with fusion drive and cancelled, because I was worried about 8 gigs of RAM being enough down the road, knowing that on the 21.5" machine RAM is not user upgradable. I specced a new 21.5 with fusion drive and 16 gigs of RAM, but am having second thoughts---it would be $1899. Now, I'm thinking about ordering a refurb 27" iMac with regular HDD and 8 gigs of RAM, knowing that I can upgrade the RAM on my own much more affordably than via Apple (which I did on my current machine) and it would be some $240 less. Despite the fact that I'm still not convinced I need that much screen real estate (which everyone says you quickly become accustomed to), it seems like a viable alternative. And, should I feel the need for speed, my question: to wit: How difficult would it be to add an external SSD boot drive? Sorry to be long-winded, and thanks for reading.