Either card will be about the max the APU can keep up with w/o suffering major CPU bottleneck. The cards are about equal in performance depending on the game and depending on the versions of each card. My factory OC Evga GTX 960 FTW was a bit faster than my R9-280, but the R9-380 is a tad faster than the 280 was. One major determining factor would be power consumption. The R9-380 is a 190W TDP card, while the GTX 960 is a 120W card. http://www.hwcompare.com/19967/geforce-gtx-960-vs-radeon-r9-380-4g/
Here at User Bench, it shows the R9-380 edging the GTX 960: http://gpu.userbenchmark.com/Compare/Nvidia-GTX-960-vs-AMD-R9-380/3165vs3482
If you have the PSU capable of handling the R9-380, and sufficient air flow for the hotter card to...
Either card will be about the max the APU can keep up with w/o suffering major CPU bottleneck. The cards are about equal in performance depending on the game and depending on the versions of each card. My factory OC Evga GTX 960 FTW was a bit faster than my R9-280, but the R9-380 is a tad faster than the 280 was. One major determining factor would be power consumption. The R9-380 is a 190W TDP card, while the GTX 960 is a 120W card. http://www.hwcompare.com/19967/geforce-gtx-960-vs-radeon-r9-380-4g/
Here at User Bench, it shows the R9-380 edging the GTX 960: http://gpu.userbenchmark.com/Compare/Nvidia-GTX-960-vs-AMD-R9-380/3165vs3482
If you have the PSU capable of handling the R9-380, and sufficient air flow for the hotter card to breathe, it may be the better choice.