Just finished with a chat with Apple to get an update. The rep briefly changed my order to expedited (which would cost an additional $27) and the Mac would theoretically arrive between the 20th and 22nd. With standard shipping, the dates are the 23rd-27th, but she said that usually the iMacs arrive towards the very beginning of those dates (and some in the UK thread are reporting that their iMacs are scheduled to arrive a day early).
If I have one minor regret, it's not going all out and getting the 1TB Flash Drive. But god was it a pricey upgrade and I have external storage (RAID) to burn. I do recommend the 4TB Seagate Backup Fast Drives -- without going SSD, the best speed you can get. Portable, bus powered.
http://www.seagate.com/external-hard-drives/portable-hard-drives/performance/backup-plus-fast-hdd/ I will eventually get an external SSD or flash drive when I need additional super fast access. USB3 is still plenty to handle those drives.
Also, the iMac takes SODIMMS DDR3L (laptop size memory) at 1.35 (low volt) and I recommend getting an additional 2X8GB for a total of 24GB. That last 8GB won't make a difference to most people. Also, the iMac ships with speed 1866 RAM CL13, but most likely supports 2133 speed. Memory will run at the slowest speed installed be it CL (lower is better) or MHz (higher is better) and there are plenty of articles debating whether speed or latency matters that much and how much it matters. If you want to go down that rabbit hole, google it! Also, some low voltage DIMMS are only market as DDR3, not DDR3L -- but look at the specs. You are looking for 1.35 volts!
Finally, it has been reported that some of the iMacs are being built here in the USofA which is awesome and should also cut on shipping time. When you report shipping, please note where you are located and where the iMac is shipping from -- and reply to your own post so we have configuration information!
PS Those of you waiting for target display mode, don't! Thunderbolt 3 still supports display port 1.2 (as well as USB 3.1) and DP 1.2 does not support target mode. So unless Apple Goes out of their way to add DP 1.3 (who knows if this will happen if they don't need it) this is what you get.
When you ordered, what your ordered, when delivery is expected. When you receive your unit, please reply to your own message. Keep specs on a single line and don't be verbose.
Just ordered 27" iMac Retina 4.0GHz i7 (6th Generation) with 512SSD (2.5 times faster than previous generation) Magic Keyboard and Magic Trackpad 2 AMD R9 395X on Tuesday 9:35 EST Arrival Available t ship 3-5 Business Days arrival October 23rd-27th