The gummint temperature recommendations are based on being able to reduce
pathogens to acceptable levels using the method which requires the least
possible skill and intelligence. So we get 165F for poultry, where 165F
achieves the required reduction in ten seconds or less, or effectively
instantaneously. It's a black and white rule, with no need for the unwashed
masses to figure anything out.
What it doesn't tell you is that there is a scale based on both time and
temperature, where the higher the temp, the shorter the time required for
the necessary amount of measurable pathogen reduction. (There is no zero
pathogen standard.)
Google "Thermal Death Time". And I've made a number of posts on RFC linking
to various official charts. If you search on my posts with "thermal death
time" you'll find them.
http://en.wikipedia.org/wiki/Thermal_death_time
Here's a chart, with includes the theory of TDT and explanation of
calculations. It may not even the same chart as I posted before, but there
is lots of this evidence to be found.
http://x2t.com/TDT
I bring this up because ideal temps for white and dark poultry meat are much
different. Breast meat held at 145F for about 17 minutes is just as safe as
165F for ten seconds. But bone in dark meat actually needs higher than 165F
to achieve proper rendering, particularly in the connective tissues. So
ideally you are looking for a method where the breast cooks at a slower
rate. Breast down, spatchcocking, separating the breast, and covering the
breast are all ways to slow down heat gain in the white meat. I've never
seen an ideal 185F thigh and 155F breast at the same time on the same bird,
but the closer you can come, the better both parts of the bird will taste
and all will be safe.
If you can actually get ideal (IMO) thigh temp of 180-185F with breast temps
of 155F, where the coolest internal breast has been at or above 155F for
more than four minutes, you will have both perfectly cooked and perfectly
safe turkey.
Alternative techniques will give better results than traditional breast up
oven roasting.
And I concur with all the other posts that you don't want to slow cook
turkey. Hot smoke roasting is the best way.
MartyB