Is it possible to crossfire an R9 280X and R9 380

Solution
The reason behind the answer is, an R9 280x is based on the original GCN 1.0 HD 7970 Tahiti GPU core, whereas the R9 380 is based on the GCN 1.2 R9 285 which is a Tonga Pro GPU core rebadged to Antigua Pro.

There are no GCN 1.0 parts in the Rx 300 series that are Crossfire compatible with an R9 280x, however you could use another 280x or even an HD 79x0.
The reason behind the answer is, an R9 280x is based on the original GCN 1.0 HD 7970 Tahiti GPU core, whereas the R9 380 is based on the GCN 1.2 R9 285 which is a Tonga Pro GPU core rebadged to Antigua Pro.

There are no GCN 1.0 parts in the Rx 300 series that are Crossfire compatible with an R9 280x, however you could use another 280x or even an HD 79x0.
 
Solution