I posted this in another thread, but I wanted to give this more exposure since my findings are somewhat buried amongst other discussion, and I'm extremely happy that it's working and figure someone else may find it useful. TL;DR #1: Dell UP2715K 5K monitor + mid-2014 rMBP 15" with GT750M = 2560x1440@2x at 60Hz, using both mDP-to-DP cables that come with the monitor! TL;DR #2: It also works with one of the two mDP-to-DP cables running through an OWC TB2 dock! Long version: after seeing the news article about the new, mid-2015 rMBP 15" with M370X supporting the Dell UP2715K 27" 5K monitor, I did a bit of searching on the Dell support site and came across this link: http://www.dell.com/support/article/us/en/04/SLN295089/EN On that page, Dell mentions the mid-2014 rMBP 15" with GT750M as a supported option in more than one place, and there is no mention of the new mid-2015 model anywhere. I decided to take a chance on it and see if the Dell support document was correct, so I ordered a new UP2715K from Amazon. The Mid 2014 MacBook Pro 15" with GT750M supports the Dell UP2715K 5K display at 2560x1440@2x at 60Hz, using both of the included DisplayPort-to-mini-DisplayPort cables! It also works just fine at 1920x1080@2x at 60Hz with DisplayPort audio (volume keys on Mac keyboard are disabled, but hardware/OSD controls on the monitor work), using just the single included mini-DisplayPort-to-mini-DisplayPort cable. As stated on the Dell support page I linked in my previous post, this is the only configuration that yields audio through the display's speakers. I did have to reboot the MBP once after first trying "5K3K" via 2x DisplayPort inputs. I toggled between 5K3K and 4K2K settings on the monitor a few times, first getting only a strange 2000-something-by-2880 resolution at 60Hz, then finally it kicked into perfect 5120x2880 native after opening and closing the MBP lid. The MBP initially gave a warning about disconnecting the USB device that was drawing too much power (only the monitor was plugged in using the included USB 3.0 cable to drive the monitor's built-in ports). After dismissing the warning and unplugging and re-plugging the USB cable again, no further warnings were issued. I tried the USB ports on the monitor, and had no issues using a SanDisk USB 3.0 flash drive. Note that the "default for display" setting in system preferences gives me 5120x2880 native; I had to select the "looks like 2560x1440" scaled option, but I can confirm that it's exactly like the 27" retina iMac (i.e., pixel-doubled, not scaled). My MBP is also running nice and cool, definitely not running scaled with corresponding heat/fan noise as you'd see on, say, a Dell P2715Q 4K display running at 2560x1440 scaled (I have one at work). For reference, my MBP is the maxed-out mid-2014 15-inch/2.8GHz/16GB/1TB/GT750M config running 10.10.3 (build 14D136). I also tested the UP2715K with an OWC Thunderbolt 2 dock. I was able to get full 2560x1440@2x at 60Hz by running one of the two mDP-to-DP cables through the TB port on the OWC TB2 dock, with the other mDP-to-DP cable and a TB cable plugged into the aforementioned 2014 MBP. Did discover one funny thing: my MBP thinks the UP2715K is an 81.5-inch display, with and without the TB2 dock inline. See attached screenshot. EDIT: after setting everything up in my home office with my vertical Henge dock and waking and sleeping the MBP a few times throughout the day, I'm having zero problems and everything is stable (i.e., no wake-from-sleep or other issues). With the TB2 dock in place now, the laptop is running slightly warmer that it does with just the display plugged in directly, but nothing outrageous and no extra fan noise. Very happy with this setup!