I'm not disputing that AMD have an advantage with DX12 games because they do; at least for the moment. This is down to the GCN architecture, which is more suited to parrallel scheduling, whereas Nvidia concentrated on serial scheduling, which was more prevalent in DX11.
The Witcher 3 and The Division are reported to support DX12, but that's not confirmed. The Witcher 3 obviously has DX11 support and I wouldn't be surprised if The Division offered both DX11 and DX12. In fact, I wouldn't be surprised if DX11 was still supported by the vast majority of games for the next few years.
OP, do you have to buy a new GPU now? You may want to consider waiting for Polaris and Pascal.