Re: Working on Speed
In college we used the technique of rhythms to increase speed and facility.
For even sixteenth notes you play them as 1-e-and-a, 2-e-and-a, etc. Now to train your brain and fingers to play faster, you can either increase tempo, or cheat a little by keeping the tempo the same and bunching up the notes in each beat in a consistent rhythm.
For example, instead of playing 1-e-and-a, play 1-tri-pl-et, where the triplet starts on the "and" of 1.. All you are doing in this example is stretching the duration of the downbeat.
Next try to stretch the "e" and then the "and" and then the "a."
After doing this for a while, you will have trained yourself to play the notes in faster succession without actually increasing the tempo. Once you do increase the tempo, you will find the original rhythms automatically much easier to play.
This works well for etudes with all sixteenths or all triplets like in the Sellner etudes. You can also apply this to your repertoire in any fashion you see fit.
I first used these techniques in the first and fifth movements of Paule Maurice's Tableaux de Province. Within a week or so, I could play these movements up to tempo, leaving the rest of my time for improving musicianship and interpretation.
I learned these techniques from Paul Cohen, Saxophone professor at the Oberlin Conservatory and Manhattan School, who told me stories of his strict technical studies with Galen Kral (an oboe professor).
Good luck. I know how frustrating those brick walls can be!