Consider the GTX780, such as the EVGA 967MHz model (ACX cooler) for about $500. That's more expensive but roughly 20% to 25% more powerful.
The GTX770 is also worth considering. The ASUS version I like is $330.
R9-280X:
Be very careful as there's a BIG DIFFERENCE between cards. The PRICE ranges between about $330 and $500. Don't get one if it's $450 or more because you are better off with a GTX780.
Also don't get a CHEAPER one which may have cooler, or quality issues.
Here's a random benchmark but it's a SUMMARY. Keep in mind the GTX780 shown is reference. The EVGA I mention is a lot better:
http://www.techpowerup.com/reviews/Gigabyte/R9_280X_OC/26.html
EVGA 780 OC/SC:
http://www.techpowerup.com/reviews/EVGA/GTX_780_SC_ACX_Cooler/26.html
*If you crunch the numbers, then the EVGA 780 SC/OC is about 24% faster than the Gigabyte R9-280X card linked above so factor that into VALUE.
Other considerations:
AMD-> Mantle
(I don't think this is going to end up a huge deal overall now that we know Microsoft has been working on DX12 to improve its performance. Game devs will want to stick with that for cross XBOX ONE/PC support.)
NVidia:
- PhysX
- Shadowplay
- Streaming (to Shield, and upcoming HDTV interface)
- G-Sync (requires new monitor).
Also, SLI is superior to Crossfire overall. Crossfire is improving though.
Summary:
Carefully consider all the above when buying a card. Again:
a) relative VALUE (benchmarks)
b) Quality (see reviews/customer feedback on any card you consider buying)
c) Some R9-280X overheating issues on some models (reduces performance)
d) Other features (mantle, PhysX etc...)