So here's an answer from Apple Care that should unsettle anyone considering one of the new iMacs. My question to them: If I were to buy the 8GB base model of the new 27 Inch iMac now, could I install my own RAM later to take it up to 64GB? Their reply: If I order the base 8GB model, while I could later install up to 64 Gb in the 4 available slots, the most that will actually be useable is limited to 16GB (for a total of 24GB). I didn't understand the explanation (I'm not techie), but it seemed to be because the original RAM was 2x4GB each, and therefore it could only deal with multiples of 4GB in expansions. My (possibly mistaken) takeaway: If you order the new 27 inch iMac with 8GB of RAM, the most you can ever useably upgrade it to is 24 GB(!) Not so, surely? Can someone who knows advise?