You are a complete idiot.
http://www.anandtech.com/bench/product/1591?vs=1442
"offers very little"
Hah. Good one.
Complete idiot? Well, notice that monitor is 60Hz, so anything over it is waste. At least I figured out that one. Also, I said Radeon R9 380 4GB, not R9 380 2GB. How do I know that is 2GB? Easy http://www.anandtech.com/show/9784/the-amd-radeon-r9-380x-review/6 Benchmarks alone are useless. Understanding them is much more important.
So this "complete idiot" owned you again. It seems that some people just cannot discuss anything civilized.
In just about every game at every resolution the 980 is offering around twice the performance of the 380, even at 1080p!
You would be insane to buy a 380 over a 980. Especially given you have up to $2,000 to spend.
Remember that monitor is 60Hz so everything over 60Hz is waste. So forget that twice performance also. Difference between ultra and high settings using 23 inch monitor is very hard to notice.
Perhaps better question is to ask why 2000$ budget machine has 120$ monitor.