lots o good advice here for all.
to the OP i would say, you should evaluate why you like and choose the works you study, i think it's a little strange that you only want to play/learn pieces that are at the limit of your abilties (interpretation and technical wise), i believe there is tremendous value in working pieces that are a good several notches below your current level so you can simply get more experience learning and interpreting new music, and so you can practice and focus on more musical challenges (phrasing, dynamics/tone) without having to wrestle with huge techinal difficulties. just a tought. i also happen to think taht some of the most beautiful music can be (and many /often times) quite simple in constrution and not neccessarily crazy difficult....
i would add a couple of things (of several) that i do and what has been helping me, how i think about the 'performance' that is, i ask myself well early inthe learning the process, 'what does success look like' with regard to learning a particular piece? I define that goal, be it an acceptable tempo, breaking through a 'barrier' or limitation I had (i.e. perhaps I was having trouble navigating works of single or multiple movements lastings more than 15 minutes of continuous /single performance playing time, etc.), then i keep that in mind as the end result and how I define the accomplishment, for me. once I achieve that, I have so much more confidence when I sit down to play it, and that helps a lot, 'knowing' you can do what you want to do helps you actually do it than 'thinking' or 'hoping' you want to.
once i have been successful, then if there is a performance (deadline or exam/jury, etc.), then I make sure that well in advance of the performance, I practice less, that is, i begin shifting the focus (as early as possible once the goals have been achieved) to practicing the performance vs practicing the piece(s). i begin no less than 1 month away (to my best ability) to begin playing the music as if it were a performance, both by myself, and (this is important) for the camera. That is, if you cannot find a mock performance opportunity (which is best), at least force yourself to record so that you put an artificial public pressure on yourself. this will help show you places that may need special polish or drilling and readdressing in front of an audience (sometimes these places will only show themselves under 'pressure').
where traditional practice is still neccessary, i begin utilizing more start and stop slow practice, that is, i play deliberately very slowsy what I am working on trying to make sure I see visually what is happening at the keybarod, where my hands are, do i have strange tension like a raised shoulder, etc, and try to remove all barriers to successful execution. then i go back and re-perform it to see if i fixed it.
i set goals for complete of these things at two weeks from the performance date, i have found that if it is not ready to be played or sounds how you want it to sound about 15 days away from the performance, you are likely not ready to perform it and every day less than 15 that it takes you to be ready only increases your odds of not having a satisfactory or your best performance.
by the time this is done, the performance becomes little more than the 'fun part' that is, enjoy the time you get to be the star! you did all the hard work and now its your turn to have a good time and share what you did with the audience. when its fun and you know you are prepared, there is little room left for thoughts that would cause crippling fear or stage fright. there will (and should) be a healthy energy or small amount of nervousnessness, thats okay i think it can help you stay sharp. but yeah by the time i sit downat the piano, and it gets quiet, and i am preparing the first note, im usualy thinking, alright guys, or hey everyone watch this, or check this out-this is going to be really cool!
in the days leading up to the performance I also try not to 'overpractice' i attemp to continue practicing theperformance (full run through, no stopping, if a mistake happens i practice being able to not look as if i made one and just move on, i also practice jumpting to memory stations if memorized or nail page turns if not i.e. collaborative/accompanying, etc). i try to make sure the night before to be super relaxed, sleep a lot, go for a nice walk or execise the day before and of, etc, basically keep stress low.