Even with 14-bit recording, I still only get about 1 EV of recoverable highlights before my exposure error becomes very noticeable.
Bit depth doesn't increase DR. Most DSLRs have ~9-9.5 stops of DR (that is, the difference between the darkest and lightest things the camera can resolve), irrespective of bit depth.
What increased bit depth WILL do for you is make it less important to expose "to the right". To illustrate:
- in a 12-bit linear system, you have 2^12 (4096) levels of grey per channel, of which half (2048) lie in the range of pure white to middle (18%) grey, 1024 lie in the next stop, and so forth. In the last stop before pure black, you have only two levels of grey, which doesn't leave much ability to describe detail.
- in a 14-bit system, you have 2^14 levels (16384) of grey per channel, of which 8192 lie between pure white and middle grey, 4096 lie in the next stop, 2048 in the next stop, and so on. The last stop between black and just-above-black is still only described by two levels (one bit), but the difference between black and "just-above-black" is much smaller on the 14-bit system. We havent said anything about what the camera considers pure black, which does speak to DR.
What this means is that for a 14-bit sensor, you can expose 2 full stops lower and still retain the same resolution as in a 12-bit system; that is, exposing to the right on a 14-bit sensor is much less necessary than on a 12-bit sensor. The DR has not increased, but your ability to resolve differences has increased and your noise floor has decreased by two stops. This isn't an increase in DR, per se, but a lowering of the noise floor; your s/n ratio has increased.