I am curious - what do you mean by 'chunking', 'dropping notes', and 'outlining'? Perhaps I use these methods in my own study but call them something else.
Very likely you do. I'll try to describe them briefly. The legendary Bernhard has done so much more eloquently than I could, so if I don't make any sense don't give up, but do a search instead.
Chunking is the selection of a short repeatable element. It may be a measure, several measures, or part of a measure. It allows you to focus on a specific technical difficulty and master it by repeating it endlessly. With the handbell choir I direct, I frequently select one measure and have them repeat it continuously until it gells. Then I add another, then combine them, etc. You have to include the conjunction in this.
Dropping notes was a revelation to me. It comes from Bernhard, not chang. Hee, hee. It is the single most effective method I've ever found for overcoming the HT difficulty. It is not so much oriented to a specific technical difficulty as it is for the general two hands coordination problem we beginners struggle with. Of course, YMMV, but it works for me. I should probably use it more often as first resort than last resort. Briefly, you select a repeatable element. You play the left hand continuously, over and over. Then you add one right hand note each time you come around. Then two. Three. Etc. Eventually you have added in the entire right hand at tempo. Then you start all over again with the right hand, adding one note at a time with the left. It may seem like this takes a long time. But it is actually faster than just starting slow and speeding up, and yields a better product. I have never had this one fail.
Outlining is something I have not personally had much success with. Maybe I needed a teacher attuned to it. Basically you rewrite the music, simplifying it, but retaining the complex fingering. For example, you take a four part Bach fugue and reduce it to a two part, but you use the same fingering you'll eventually use with four. This is supposed to be highly effective, but my efforts have not been very successful, so probably I"m doing it wrong.
I am also curious as to what makes working up to speed the LEAST efficient practice method. It works well for me, but maybe I take longer to learn pieces than I should.
Not all methods of working up to speed fail. But starting slow and working up incrementally is often recommended, yet also decried by the better teachers. It is inefficient, because you spend too much time working at easy tempos for the majority of the piece. And it is dangerous, because you can build speed walls. But my main objection is philosophical. It contains an element of magical thinking, whereupon "paying your dues" is rewarded with success. And that just doesn't happen in the real world.
I hope I haven't offended. It was never my attention to attack you personally. My objection is to the slow speedup method, and that may not be what you are recommending.