Shot noise is a physical limitation, not a man made one. The man made
limitations can be improved upon.

Nice plot.  If you look at my past posts, you would also see that
I've said for at least a couple of years 14-bit or higher A/D are
needed too because current DSLRs are limited by 12-bit converters.
Some attacked me in this NG with the idea that "if more than 12-bits were
really needed, then why haven't camera manufacturers done it?"
We'll we now see they have, and I'm sure 14 or more-bits will become a
new standard in future DSLRs.

Regarding fixed pattern noise versus photon Poisson noise, your plot
and some simple illustrations show what is dominant.  First clue,
look at the thousands of images on the net.  How many show fixed
pattern noise?  It is very rare.  You tend to see fixed pattern noise
at the very lowest lows in an image.  Second, if fixed pattern noise
is really a factor, guess what, you can calibrate most of it out with dark
frame subtraction.  I think good examples of fixed pattern noise is
illustrated at:
http://www.clarkvision.com/photoinfo/night.and.low.light.photography
Figure 1, for example shows two merged low light images and fixed pattern
noise is not apparent, nor is it the dominant noise source in the image.
Figure 2 shows the black sky above the Sydney opera house in an ISO 100
20 second exposure.  Fixed pattern noise is a little over 1 bit out of 12
in the raw data.  It simply is not a factor.  But where the scene has
signal, e.g. the lit roof, noise is proportional to the square root
of the signal strength, with photon noise up to 18 out of 4095
in the 12-bit raw file.  So, over most of the range, photon noise
dominates.  The low end, the bottom few values or bottom couple of bits,
is a combination of photon noise, read noise, and fixed pattern noise.
That gives about 10 bits out of 12 with photon noise as the dominant
noise source.  Again, if you work at the low end, calibrate out
the majority of fixed pattern noise with dark frames.

Let's work an example.
Let's assume fixed pattern noise is more objectionable by
10 times random noise (this is a reasonable estimate
for me, and I find fixed pattern noise quite objectionable).
But then with processing, e.g. dark frame subtraction, it can
be reduced about 10x, then filtered and reduced more, all with
minimal impact on resolution.  Random photon noise in an image
from can only be reduced by pixel averaging, thus reducing spatial
resolution.

Let's use your full well depth, rounding off to 53,000 electrons.
Fixed pattern noise in DSLRs like the 20D and 1D Mark II are between 1 and
2 bits in the A/D at low ISOs.  At low signal levels, line-to-line
pattern noise is on the order of 7 electrons in the 1D Mark II, with
low frequency offset of a few tens of electrons (at ISO 100 fixed pattern
noise appears at about the 1-bit level, which is ~13 electrons.  The low frequency
fixed pattern noise is entirely eliminated by a dark frame subtraction,
and line-to-line (what you call 1D) is reduced by about 10X with
dark frame subtraction.

So there are multiple conditions.  Here is one example:

ISO 100, 1D Mark II, 53,000 electron full signal:

     Signal      Photon noise    Read Noise  Fixed-pattern  What noise dominates
(elect-  stops   (electrons)    +A/D noise    noise         Photon, read, or pattern
 rons)                          (electrons)  (electrons)

53,000    0        230             17           ~13          Photon
12,250   -4        110             17           ~13          Photon
 3,312   -6         57             17           ~13          Photon
   828   -8         29             17           ~13          Photon
   207  -10         14             17           ~13          all 3 similar
    51  -12          7             17           ~13          read + pattern

The above table demonstrate the the sensor has noise dominated by photon
statistics over most of its dynamic range.  Each generation
of cameras that comes out pushed the floor where other noise sources in the
electronics show.  It is likely we'll see the 1D Mark III push those limits
a stop or two lower.  But photon noise remains and is the ultimate
limit.

Here is another test series that illustrates the above conclusions:
 Digital Camera Raw Converter Shadow Detail and Image Editor Limitations:
 Factors in Getting Shadow Detail in Images
 http://www.clarkvision.com/imagedetail/raw.converter.shadow.detail

Figure 6 shows areas from +2 to -7.6 stops.  But if you look at the different
raw conversions, you'll see widely different results and wildly different
fixed pattern noise.  Then look at Figure 16: the camera jpeg looks pretty
clean with less pattern noise than some of the raw conversions.
So when you say you don't believe photon noise versus fixed pattern noise,
understand the effects of converters too.

Roger

And that is why people who evaluate sensors do more than simply
study the standard deviation of one image.  To understand noise sources,
the standard procedure is to make a series of exposures and analyze
the results from the different test conditions.  e.g.:

 The Nikon D50 Digital Camera:
 Sensor Noise, Dynamic Range, and Full Well Analysis
 http://www.clarkvision.com/imagedetail/evaluation-nikon-d50

http://www.clarkvision.com/imagedetail/long-exposure-comparisons/index.html

and more at:
http://www.clarkvision.com/imagedetail/index.html#sensor_analysis

other:
http://www.astrosurf.org/buil/20d/20dvs10d.htm

Roger