Despite some social media complaints to the contrary, the forthcoming iMac Pro appears to be very competitive with rivals' offerings, and also against those seeking to build a machine out of parts matching specifications and parts.
Little is still known about the "entry-level" iMac Pro, regarding technical specifications. For $4999, users get an undeclared 8-core Xeon processor, four Thunderbolt 3 ports, four USB 3 ports, a single 10-Gig Ethernet port, 1TB of SSD storage, 32GB of 2666 MHz ECC RAM, and as-yet unreleased Vega graphics.
Imgur member "Squaruss" posted a comparison to a Lenovo workstation. The build included an 8-core E5-2620 v4 processor, a P910 motherboard with two Thunderbolt 3 ports, 32GB of 2400MHz ECC RAM, a Nvidia Quadro M5000 GPU, two 512GB M.2 PCI-E SSD in RAID configuration, a SD card reader, 802.11ac wi-fi, and a 1300W power supply listed as 92 percent efficient. No 10Gbps Ethernet option was available for the workstation, but the build includes a pair of Gigabit Ethernet ports.
The build price by the Imgur member was confirmed by AppleInsider and totaled $5394, after a $599 "instant savings" discount which appears to be a limited time promotion. Notably, a monitor was absent from the build.
A second "DIY" build was posted by PC Gamer. In the second build, the publication implements the same processor as in the Lenovo build, downgrades storage speed to a single 1TB 960 Samsung EVO SSD, cuts back the Thunderbolt 3 ports to one with a PCI-E card, uses the integrated Gigabit Ethernet board on the motherboard, downgrades the power supply to 1000W which might be too low for reliability, and downgrades the video to the GeForce GTX 1080 Ti.
AppleInsider confirmed the $4687 bill of materials on the PC Gamer build. However, it includes about $100 in rebates which are accounted for in the price, and also incorporates the LG Ultrafine 5K display for some reason. Given that it would not be accelerated by the GTX 1080 Ti and would only be in 4K resolution on Windows, its inclusion isn't clear.
A better solution, but still not ideal given the dire Windows 10 5K situation at present, would be the now-discontinued Dell UP2715K 5K display, for about $1500 used. The addition of the Dell monitor adds $300 to the bill, for a total of $4987 -- within $12 of the iMac, with compromises.
A $120 retail Windows 10 license isn't included with the PC Gamer piece, nor is any consideration for the "cost" of the user's labor to assemble the computer.
Both the Lenovo and DIY configurations are tower builds, with two PCI-E slots remaining on the Lenovo build and one on the DIY -- which the iMac lacks. Four Thunderbolt 3 ports on the iMac Pro double that on more generous Lenovo build, and one on the DIY build is no comparison at all.
Other "boutique" PC vendors' websites were also checked by AppleInsider, with prices ranging from $5225 to $8250 for an assembled and configured unit, with similar specs to the iMac Pro. Depending on the vendor, shipping adds up to $100 to that price.
The elephants in the room
The bills of material examined are current as of June 9 at 10:00 a.m. eastern time. PC part pricing fluctuates a great deal, with things like RAM acting more like commodities, seeing weekly and monthly cost shifts up and down. But, over time, the costs of the PC parts on the builds will be on a mostly linear trajectory downward.
The PC build, and the Lenovo workstation can be had now, without having to wait for the iMac Pro.
Presumably, Apple isn't going to wait four years to update the parts or pricing on the iMac Pro like the Mac Pro, but Apple hasn't ever made a computer quite like it before. For this, history is a bad judge one way or another.