While the iMac lacks an SSD to get full benefit from the High Sierra update, it does have a hardware advantage when it comes to encoding HEVC videos in 10-bit colour.
From Ars Technicha: Only Macs with Skylake and Kaby Lake processors support hardware-accelerated encoding and decoding of HEIF and HEVC files at all; this covers all Macs introduced in 2016 and 2017 and 5K iMacs from late 2015. Only the Kaby Lake processors in 2017's Macs support hardware decoding of HEVC videos with 10-bit colour, one of the few new features that separated Kaby Lake from Skylake in the first place.