Having purchased an rMBP 13" (8/256) a couple of months ago and loving it ever since, I'm seriously looking at the 5k iMac. The CPU is a no-brainer - quad core i7. What I can't decide upon is whether it is worth getting more than 8 Gb RAM, and upgrade the 290X to the 295X. First, the memory. On my rMBP it does use the swap file (most I've seen is 400 Mb), but because it is SSD backed, the performance hit (if there is any!) is unnoticeable. Is it worth upgrading from 8 Gb to 16 Gb? The "memory pressure" graph is usually less than half at any time. I have a graphics-intensive Java application that pushes this to maybe 2/3 the way, but this was when I was testing it and opened everything I could. Performance seemed excellent even when I tried to kill it. Second, the GPU. Yes, I will want to do gaming on the iMac. That said, my current PC has 2 Gb graphics card (2 Gb AMD R290) which I understand is very close to the M290X found in the iMac. I'm very happy with this card in my PC. Looking at raw tech specs, the M290X posts higher fill rate than the M295X, so it seems the only real difference is the video memory. Allowing for the fact the iMac is pushing 5k, is there really any difference between the two cards? In other words... is the 295X worth the extra $300? It would seem not. Regarding the storage, apparently if you go SSD it is soldered to the board, but if you go Fusion drive you can replace it with OTS SSD? Is this correct? If so, is it worth doing? Any suggestions for running external storage via Thunderbolt? At the moment I use a network share for most stuff, and a USB drive for TM backups.