Yeah, it really is going to come down to price.
As for the gpus, I think it's awesome that there are going to be some powerful options and 2 of them at that. However, developers still dictate which hardware will run software best. So while Apple has thrown its weight behind OpenCL, certain programs still perform much better with CUDA or even just NVIDIA cards versus their AMD counterparts. Of course that can change and I've seen that Adobe has promised OpenCL support for Premiere. But it could be a long long while before other programs do the same. And in the case of Adobe, I'll have to subscribe to CC in order to get the updates. Autodesk, Avid, and everyone else? Who knows?