The iMac "Core i7" 4.0 27-Inch Aluminum (Retina 5K, Late 2015/Skylake) technically is
a "configure-to-order" configuration of either the iMac "Core i5" 3.2 27-Inch Aluminum (Retina 5K, Late 2015/Skylake) or iMac "Core i5" 3.3 27-Inch Aluminum (Retina 5K, Late 2015/Skylake),
but also is documented as a separate model for reader convenience.
Other than processor (and the corresponding level 3 cache), this custom model is identical to its stock counterpart.
The iMac "Core i7" 4.0 27-Inch Aluminum (Retina 5K, Late 2015/Skylake) initially featured
a 14-nm "Skylake" Quad Core 4.0 GHz Intel "Core i7" processor (6700K) with
four independent processor "cores" on a single chip,
an 8 MB shared level 3 cache,
8 GB of 1867 MHz LPDDR3 SDRAM (PC3-14900) installed in pairs (two 4 GB modules),
a 1 TB or 2 TB "Fusion Drive," and
an AMD Radeon R9 M390 or AMD Radeon R9 M395 graphics processor with
2 GB of dedicated GDDR5 memory.
It also has a built-in "FaceTime HD" webcam and stereo speakers.
This model has a 27" 5120x2880 LED-backlit 16:9 widescreen IPS DCI-P3 "Retina 5K" display.
The rear of the case is aluminum and is thicker in the middle and tapers to a razor thin 5 mm at the edges.
four USB 3.0 ports,
dual Thunderbolt 2 ports,
802.11ac Wi-Fi (802.11a/b/g/n compatible),
and Bluetooth 4.0.
Compared to its predecessor, this model essentially has the same external enclosure, but it has a higher quality DCI-P3 "Retina 5K" display with a wider color gamut as well as a more advanced architecture and graphics architecture.
Please note that stock images are used