The potato is probably not as important as the method. Simply frying them will not get you the fry you want. Basically you boil them, then double fry them. Here are the steps for The Perfect French Fry:
Ingredients
2 pounds russet potatoes (about 4 large), peeled and cut into
1/4-inch by 1/4-inch fries (keep
potatoes stored in a bowl of water)
2 tablespoons distilled white vinegar
Kosher salt
2 quarts peanut oil
Procedure
Place potatoes and vinegar in saucepan and add 2 quarts of water and
2 tablespoons of salt. Bring to a boil
over high heat. Boil for 10 minutes.
Potatoes should be fully tender, but
not falling apart. Drain and spread on
paper towel-lined rimmed baking sheet.
Allow to dry for five minutes.
Meanwhile, heat oil in 5-quart Dutch oven or large wok over high heat
to 400°F. Add 1/3 of fries to oil (oil
temperature should drop to around
360°F). Cook for 50 seconds, agitating
occasionally with wire mesh spider,
then remove to second paper-towel
lined rimmed baking sheet. Repeat with
remaining potatoes (working in two
more batches), allowing oil to return
to 400°F after each addition. Allow
potatoes to cool to room temperature,
about 30 minutes. Continue with step
3, or for best results, freeze
potatoes at least over night, or up to
2 months.
Return oil to 400°F over high heat. Fry half of potatoes until crisp and
light golden brown, about 3 1/2
minutes, adjusting heat to maintain at
around 360°F. Drain in a bowl lined
with paper towels and season
immediately with kosher salt. Cooked
fries can be kept hot and crisp on a
wire rack set on a sheet tray in a
200°F oven while second batch is
cooked. Serve immediately.
Worth reading is also the science behind the perfect fries.
Unless you are prepared to build some industrial strength equipment of your own design and then move everyone in the neighborhood away while you experiment with this, I fear you are taking your life in your hands.
Normal pressure cookers add a maximum 15 PSI to achieve a water boiling point of 121 C or 250 F. Autoclaves, used for surgical sterilization, go to 30 PSI. You are talking about going more than twice that.
There is no reason, based on the science of Maillard reaction, to believe that it would not occur at a high enough temperature. The presence of excess water would normally inhibit the process because of temperature reduction, but your "super duper pressure cooker" would keep the temperature at a high enough level to allow the chemical breakdown to occur. You might, in fact, discover that it occurs a bit earlier, as water tends to facilitate many reactions. Caramel making comes to mind as an indicator of what might be achieved, as sugar syrup (OK, most of the water is gone, but in principal) browns when you get in the above 330F-165C degree range.
As to crisping based on quick pressure reduction (perhaps when your device explodes?) That seems less likely as most crisping comes at the loss of water, and you are, in effect, keeping water in contact with your food both in liquid and superheated steam form. It would, most likely, be similar to a braised food surface, than a fried one.
Interesting thought. Please don't try this.
Best Answer
The matter here is much more complex than simple "drying out". Starch physics is complicated stuff, and I don't know it in all details, but here is the rough picture.
Starch starts out in tiny granules in the plant. When it is soaked in water and then heated, there is a temperature at which it rapidly turns from a starch suspension (if you had free starch) to a colloid (starch gelatinization). The theory is that these tiny granules burst, but I don't remember if it is proven yet.
At that point, the starch colloid is at its softest. It starts slowly losing water and recrystalizing (starch retrogradation). You can best see it in standard French bread - if you try cutting into it in the first hour after coming out of the oven, you get squished gluey crumb. After that it is soft like cotton for several hours to a day, but gets drier and harder. On the next day, it is already quite dry, and soon after it becomes stone hard.
Just like the gelatinization process, the retrogradation is also temperature dependent. And it happens to work quickest at fridge temperatures. It is slower at warm temperature, and stops when frozen.
So, your goal is not simple dehydration, and other dehydration methods will not really help you much here. You have to stick with what works, and that's temperatures just above freezing.