Apple's 5K iMacs have been extremely popular, especially with content creators, and this year's hardware refresh packs in even more bang for the buck. If you're trying to decide between buying the latest model, or a discounted late 2015, AppleInsider offers a closer look at how they compare.

Externally, the 2017 iMac is basically identical to the 2015 version apart from the replacement of two Thunderbolt 2 ports, which have shifted to Thunderbolt 3 with USB-C connectors. Thunderbolt 3 is a huge step up from Thunderbolt 2, as it's not only twice as fast at up to 40Gb/s, but can adapt to almost anything including a single 5K or two UHD 4K displays.

The 2015 iMac can technically support an external 5K display, but it has to be a dual DisplayPort model that will take up both of your Thunderbolt 2 ports and limit output to 8-bit color. 

Apple boasts a 43 percent increase in display brightness, but unless your Mac is in a very bright room or you're battling glare, you won't need the extra nits. In my well lit office, we ran the 2015 model one to two bars shy of max brightness, compared to four to five with the 2017 model. 

So what's the verdict? Well if you're planning to edit video with Final Cut X, render using OpenCL or spend time gaming, the 2017 i7 Kaby Lake iMac with the 8GB Radeon Pro 580 provides a massive performance improvement over the previous iMac. It's definitely worth buying the new model over a used or refurbished one, and if you own a 2015 and make a living with Final Cut, it's worth selling and upgrading since Macs hold their value so well. 

If you're a photographer or edit video with Premiere Pro, it's really not worth upgrading. With that said, if you're comparing both models, the 2017 is still a better value since it now sells for $300 less in the best configuration with 32GB of RAM and a 512GB SSD (see how to save an additional $75 with exclusive coupon code APINSIDER, plus no tax collect on orders outside NY and NJ, at Adorama). 

If you're working with Adobe programs and don't game, you can save some money and go for the mid tier i7 with 4GB 575 graphics since these programs don't make use of the better GPU, but are more CPU limited. This configuration will outperform the best available options in 2015 with a $400 lower price tag. On top of that you get the benefits and future proofing of Thunderbolt 3, with a brighter display and lower fan noise. 

Source: appleinsider