I guess this picture sums it up.Great write-up. I used to play with cascade phase change cooling during the P3/P4 and Core 1/2 days, and while I never personally took the dive into LN2 I still keep up with the XOC community. It's an entirely different game from standard air or water based overclocking.
Rather than trying to minimize thermals you begin to run into actual hardware limitations, as well as material property challenges. From power to humidity, cold bugs, broken multipliers, frequency holes and dozens of other new and interesting problems.
Multi core processors like this are less of a drag race and more of a tractor pull. I love it.
It really does become half art, half science. But it's always wholly fun to follow.