The late 2013 refresh is far from revolutionary, but coming less than a year after the radical redesign of November 2012, it hardly needed to be. The processors moved over to the new fourth-generation Haswell chips, and these 27-inch models get a small clock speed increase not enjoyed by the 21.5-inch iMacs.
The graphics processors are now Nvidia 7 Series GPUs, and the WiFi is now 802.11ac. If you opt for a solid state or Fusion drive, a PCIe connector is used for a further improvement in speed.
There's plenty to like about the late 2013 27-inch iMacs. The new processors prove their worth in our benchmarking tests, and although the off-the-shelf Core i5s lack a Hyper Threading feature, Turbo Boost gives them a welcome burst of speed when needed.
The new graphics processors are very welcome too, especially as they enjoy double the onboard memory of the previous generation's. Although the optical drive had to be sacrificed for the new slimline design, if you still use optical discs, it's easy to add on an Apple USB SuperDrive, and the external solution is more ergonomic than the pre-2012 iMac's method of mounting them on the side of the panel.
Also, unlike the 21.5-inch iMacs, here you can upgrade the onboard RAM yourself, quickly and easily.
We've few complaints about the 2013 refresh. They're expensive, of course, but not poor value for money. The fact that the cheaper 27-inch model increased in price by more than the rest of the range is offset by its step ahead in processing and graphics power, breaking the spec parity with the more expensive 21.5-inch iMac.
Although being able to add more memory after purchase is welcome, very little else about the 27-inch iMacs can be upgraded. The fact that the screens are now glued to the bezel instead of being held in place with magnets as they were before the 2012 redesign means the latest iMacs are difficult to upgrade even for qualified technicians. This could prove really annoying if your internal hard drive should fail.
The 2013 refresh is a solid, if unremarkable, update for Apple's most popular desktop computer. It wasn't a radical overhaul, but nor did it need to be. Instead, the specifications got a welcome boost while retaining the well received form factor of the previous generation.
The £50 increase in the cost of the more expensive 27-inch model is simply inflationary, while the £100 price hike for the cheaper one is justified by the advances it makes. An excellent refresh.