That's so funny you mention the GTX 1060 being about $250 because earlier today I was going to bring up the idea of Nvidia hitting that price point. I'm not so sure if that is a smart, average, or dumb move on their part. The large price gap between the GTX 960 and GTX 970 was probably the reason why so many GTX 970s were sold. People are like, "eh, not sure the GTX 960 has the performance I am looking for. Oh crap, the GTX 970 costs $150 more? Ah well, I guess it's just better worth it. I'll get the GTX 970." Now, though, if the GTX 1060 is priced at about $250 people may pass on the GTX 1070, making Nvidia lose some money. Then again, it really depends on the performance of the GTX 1060.
If the GTX 1060 costs 25% more than an RX 480, you would expect it to have 25% more performance. I don't feel this will be the case, though, as that will give it a huge benefit over the GTX 1070 in the price/performance arena. I think the GTX 1060 will probably have about 5-10% better performance than the RX 480, giving it less price/performance than both the RX 480 and GTX 1070, but will probably sell more because Nvidia. Since it will have less price/performance than the GTX 1070, people will still make that jump to the 1070 so Nvidia will get their cash, but those budget-conscious people who will just get the GTX 1060 will still give Nvidia more money opposed to it costing around the RX 480's $200 price point.
If the GTX 1060 costs 25% more than an RX 480, you would expect it to have 25% more performance. I don't feel this will be the case, though, as that will give it a huge benefit over the GTX 1070 in the price/performance arena. I think the GTX 1060 will probably have about 5-10% better performance than the RX 480, giving it less price/performance than both the RX 480 and GTX 1070, but will probably sell more because Nvidia. Since it will have less price/performance than the GTX 1070, people will still make that jump to the 1070 so Nvidia will get their cash, but those budget-conscious people who will just get the GTX 1060 will still give Nvidia more money opposed to it costing around the RX 480's $200 price point.