I'm speaking rhetorically, by the way. this is meant more to make you think. You shouldn't suffer from a bottleneck, you shouldn't worry about bottlenecks (unless you're taking extremes like a dual-core Xeon or slowest quad-core possible with a 1080 Ti), and you shouldn't downgrade the GPU just because a few of today's games are held back since they will get tougher to drive in the coming months.
GTAV, BF1, and Some Other Games would be GPU-dependent aside from a few areas in GTAV like the beach/boardwalk and shopping district.
WD2 would be CPU-dependent as it likes fast cores for single-threaded functions and the AI engine loves as many cores as it can take.
Ram speeds don't work like that. If you have 1x DDR3 at 789mhz + 1x DDR3 at 2100mhz, you will not get 2889mhz. If you buy another 4GB HyperX Fury DDR3, you'll have 8GB Ram total running at whatever the LOWEST speed is, so if 1x 789mhz and 1x 2100mhz, both will be 789mhz.
I've researched it, unfortunately the Fury does not come with XMP, and normally it should automatically clock itself to 1866, are you sure you have auto set in bios for ram ? but if you want just go to bios and change the frequency to 1866, you may have to mess with timings as well for stability, you have them there in SPD.
CPU-Z seems like it only shows the last 4 profiles stored in the memory stick. The last one for your memory is JEDEC #8 888 Mhz (1776 Mhz) which is probably there for compatibility reasons because there's already a better profile JEDEC #6 which lists the same frequency but lower timings (888 Mhz 10-11-10-29-40)
So you know for sure the memory can do 1776 Mhz at 10-11-10-29-40 , and since it's sold as 1866 Mhz it will most likely be able to work at 1866 Mhz (933 Mhzx2) - it's not a big step up from the JEDED #6 profile.
However since it looks like the memory stick does not have a profile for 1866 Mhz, you may have to go in BIOS and configure the frequency manually to 1866 Mhz and you may also have to adjust the timings because the ones currently set are for 1600 Mhz and at 1866 Mhz these may not work.
As the ram says it can do 10-11-10-29-40 at 1776 Mhz, it should be capable of working with these at 1866 since it's not a big step up but simply because I'd just want to get it workind and not worry about it, i would start by slightly relaxing the memory timing to 11-11-11-29-40 - there wouldn't be much difference in real world use, you wouldn't feel a difference using these slightly slower timings.
I'd keep the voltage the same standard 1.5v .. if it can do 1776 Mhz at 1.5v it should do 1800 Mhz as well.
So basically, write down on a piece of paper 1866 Mhz and 11 , 11, 11, 29 , 40 and what each means (copy the column on the right)... then go in bios at memory and set those parameters to the proper values, save and reboot.
If you want to make sure the memory works OK , you can create a bootable USB disk or CD with memtest : http://www.memtest86.com/download.htm
You boot from it and will automatically run some tests on the memory (test runs for probably more than about 15 minutes and then loops so once it completes a full test you can just turn off your pc).
If you have memory errors, you may want to raise the voltage to 1.55v from the standard 1.5v just in case the memory chips can't handle the higher frequency at the default voltage and run the test again.
If you still get errors, could be the motherboard just can't do 1866 Mhz with 2 x 8 GB memory sticks so you should just let it go and set it back to 1600 Mhz