I'm in the Exact same boat as you. One thing that I can tell you is to stay away from dell/alienware.
Which leaves you with the GT73VR 7RF Titan Pro -VS- Sager NP9873
GT73VR 7RF:
Intel Core i7-7820HK Quad Core Processor 2.9 GHz
17.3" Full HD 1920 x 1080 @120Hz 5ms, Matte, G-Sync (Anti Glare) TN Panel Screen (very high quality - IPS Level)
Mobile Intel® CM236 Express Chipset
32GB DDR4 2400MHz RAM
512GB (2x 256GB SuperRAID) SSD + 1000GB 7200RPM HDD
GeForce GTX 1080 8GB Graphics
USB3 | HDMI | Bluetooth | DisplayPort | SD Card Reader | Thunderbolt 3 / USB Type C
Killer Wireless-AC 1535 + Bluetooth 4.1 Combo Card
Killer Gaming E2500 Gigabit Ethernet Controller
Full Colour Backlit Keyboard
Sager NP9873
Intel Core i7-7700K DESKTOP Quad Core Processor 4.2GHz
17.3" QHD 2560x1440 @120Hz 5ms, Matte, G-Sync (Anti Glare) TN Panel Screen (very high quality - IPS Level)
Mobile Intel® CM236 Express Chipset
16GB DDR4 2400MHz
256GB M.2 SSD + 1000GB 7200RPM HDD
GeForce GTX 1080 8GB Graphics DESKTOP
USB3 | HDMI | Bluetooth | DisplayPort | SD Card Reader | Thunderbolt 3 / USB Type C
Killer Wireless-AC 1535 + Bluetooth 4.1 Combo Card
Killer Gaming E2400 Gigabit Ethernet Controller (RJ45)
Full Colour Backlit Keyboard
In my opinion, 1440p is nice. But there is nVidia DSR for Upscaling on the MSI which might not be Pure 1440p but on a 17" screen, the difference between upscaled 1440p and true 1440p is minimal. I've tested it. In terms of performance, Sager wins because of the true desktop grade CPU/GPU but not by far at all. One thing to keep in mind is that they get hot. Real hot. I mean up to 90* Celsius hot. If you're planning to have this laptop for a while, then consider newer games that will come out and give the 1080 a run for it's money. Running 1440p resolution in a year or two years time, you'll probably have to change resolution to 1080p if you want over 60. From my experience, MSI are built better. And the new chassis with Cooler Boost will remove a good 20C from your gpu/cpu if they get hot. The Audio that MSI has is incomparable. Remember that 1440p on Laptop is still in its early stages. 1080p is well established and the quality on 1080p is near to perfect.
I'm in the UK so my only option is to go with MSI, but not sure where you are. If you're in the US then I guess you can get Sager, and if not. Remember that if Sager has a fault, then you'll have to ship it back to the US for repair. Hope this helps.