After seeing the new iMac with Retina 5K display (I'm just going to call it a Retina iMac from here on out, or even riMac for short), I decided it was time to upgrade my aging but still oh-so-functional mid-2011 27" iMac.
For those contemplating the same upgrade, you may be mulling decisions on processor, RAM, storage, and graphics cards; here's the logic behind each of my choices in those areas, in case it helps you with your decision.
This was the simplest decision to make—I always buy the most powerful CPU I can afford. In the case where the choice is a Core i5 vs. Core i7, I will always go for the Core i7. That's because only the Core i7 supports hyper threading, which, as Apple writes, is "a technology that allows two threads to run simultaneously on each core. So a quad-core iMac has eight virtual cores, all of which are recognized by OS X. This enables the processor to deliver faster performance by spreading tasks more evenly across a greater number of cores."
In addition, by upgrading the CPU, I make the machine more usable many years down the road—whether for my own use, or when reselling to someone else.
This is where you can save some money, but it can also be complicated by market pricing and compatibility issues. But after some Twitter exchanges, I chose the stock 8GB configuration, with a 16GB memory kit (from Crucial or Newegg or similar). This will give me 24GB total RAM, for about $180 more than the base configuration.
Compare that with Apple's pricing, which is $200 to add only 8GB of RAM (i.e. to go from 8GB to 16GB). Things are even worse with the 32GB option, which is listed at $600 (to net add 24GB). Third party 32GB RAM kits are about $330.
Basically, if the RAM is user upgradeable, you'll save a lot of money by buying and installing it yourself. And because the 27" iMac has four user-accessible RAM slots, if you take the stock configuration (two slots filled), you can add two sticks of your own—and then, down the road, if you need more, replace the stock Apple RAM.
For most people, this may be the trickiest choice to make. Fusion drive or SSD only? How big? The answer will be highly personal. For me, though, it was pretty straightforward. I have a 256GB SSD in my current iMac, and it's only about half full. I keep most of my applications, and all of my audio and video files, on an external RAID array, so I don't need a lot of internal storage.
What to buy depends entirely on your needs, of course; the stock 1TB fusion drive may be more than enough for your usage. However, if I were ordering and didn't have the external array, I'd probably go for the 3TB fusion drive—it's only $150, and promises lots of room for future growth (and will help resale).
In aviation, there's a saying that goes "You can never have too much runway in front of you." I have similar feelings about graphics cards: bring on the power! In this case, given that the graphics card is pushing 14+ million pixels, doubling the VRAM to 4GB seems like a prudent thing to do.
I was able to find a bit of information on these cards, and the M295X seems appreciably faster than the M290X. And again, faster is better when pushing lots of pixels.
Finally, as with the CPU and storage decisions, a faster video card should help resale value in the future.
So that's what I ordered; I'll follow up with some real-world experiences once I have the machine in late October/early November.