While the audio DSP does not contribute to the architectural efficiency it does increase the area and thus cost of the chip regardless. At present it has limited/no use but costs AMD to implement.
Yes but any additional cost Bonaire has to manufacture due to die size has been gained back
and then some due to the extra 11 months of manufacturing. Remember too that there was only one Bonaire SKU at the start, so all the good Bonaire chips were maximum price - this isn't the same with GM107 which has the Ti and non Ti version.
This is part of what sushi meant when talking about AMD going for perf/$ instead of perf/W. You can make more "working" chips with more variability, and that's exactly what AMD has done with Bonaire. Nvidia has split GM107 by having a clear good part and one "not so good", right from the start. For all we know the Ti version might only be 20-30% of all the working chips coming off the wafer. Even if it's 80%, you can still see how having 20% of the lesser version is a drawback compared to AMD having one "Bonaire XT" SKU commanding full price for 3 quarters of a year.
Even now Bonaire probably has more revenue per wafer than GM107 (at $120 prices vs GM107's $150) - even with GM107's smaller size. A year ago Bonaire was one SKU with 896 shaders at 1GHz. Now it has 2 SKU's - one with 896 shaders at 1100MHz and one with 768 shaders at 1GHz. In other words, they are definitely getting more useable chips out of the same wafers.
Now if you consider the R7 265 at $150 - Pitcairn has been around for 3 years and this is basically the worst part that they throw out now. Yield must be as close to maximum as you're gonna get - and it's a salvage part of a much more expensive chip.
The point is, time to market counts way, way more than die size here. If AMD chooses to fight Maxwell with old, cut down chips that aren't *that* much bigger then they are clearly able to do so.
Really, the 750 Ti is a nice card but the price is completely out of whack...cuz Nvidia. It should be $100, putting huge pressure on whatever AMD has down there now. Problem is they would then have to drop the price of the 640.
If the 265 does find itself at $150 at retail, you can be sure that the 750 Ti will drop by at least $20.