I'm in Toronto, Canada
Ordered the following config on June 5th:
i7 4.2/ 8GB RAM/ 512 SSD /Radeon 575
Ordered the Crucial 32GB kit (2x16GB) from B&H:
https://www.bhphotovideo.com/c/product/1208371-REG/crucial_ct2k16g4sfd824a_32gb_ddr4_2400_mhz.html
Changed my mind (argh!) and on June 10th ordered the following:
i7 4.2/ 8GB RAM/ 1TB SSD /Radeon 580
June 5th order arrived from California (via Fedex) on June 14th. I sent it back without opening the box.
June 10th order arrived today! It's the fastest computer I have ever used. My work machine is a fully loaded 13" i7 2015 MBP but I have been holding on to my 24" iMac Early 2008 with transplanted 512 SSD (Samsung 840) at home for what seemed like an eternity. This new iMac is a beast and the screen is so beautiful. I have to double-check that the task I asked it to do was completed because it happens so fast!
RAM works perfectly and I ran Apple diagnostics (hold D on boot) to verify.
Popped my Samsung 840 into a USB 3.1 Gen2 case and it's running faster than when it was in my old iMac as it was being held back at 3.0Gbps SATA 2 speeds. I used this case:
https://www.startech.com/HDD/Enclosures/usb-3-1-drive-enclosure~S251BPU31C3
I've been lurking since I placed the first order on June 5th but I'd like to say thanks to all the folks that posted their findings on here.