The i3 4370 will not bottleneck the R9 280, despite the i3 being a duo core CPU. I prefer going with the i5 because it is so powerful and it being a quad core.
The R9 280 has better performance and has more VRAM than the GTX 960. The R9 280 has a higher texture rate, more shading units, texture mapping units, and a wider memory bus.
The i3 4370 will not bottleneck the R9 280, despite the i3 being a duo core CPU. I prefer going with the i5 because it is so powerful and it being a quad core.