This gets a little bit off the specific topic of counting notes in X notes per string in Pebber`s syllabus. I decided to break the ice on this forum by sharing the different counting methods I`ve encountered.
With regard to having trouble counting the notes at high tempo, I have the same problem occurs if I try to vocalize the words "One, two, three...etc" in my head. Especially when you hit the 2 syllable "Seven". This is even worse when saying it aloud. I am pretty bad with tongue-twisters which does not help! I always end up focusing on not-screwing-up-my-count and not on what I`m playing.
When I practice, say, 5 notes per string at low tempos, I just think (or say) the name of the number. I accent the "One" in each count. Once the tempo is higher I just think of a single syllable (such as Tick) and accent the first note that syncs up with the beat. After that I might focus on the pick hitting alternating between Up and Down on the beat. Taping alternating hands on a table slowly and focusing on which hand hits on the beat is a good way to get in tune with alternating your pick stroke and not worrying about how many notes you are hitting per beat, once you get a feel for the tempo.
My old teacher used to tell me to think of the word "University" when playing 5 notes per beat. "You-nee-ver-seh-tee". That sometimes helps me get the ball rolling quickly if switching from another X notes per beat exercise. You have to make sure you don`t add that extra note at the end!
When I did music in grade school we always counted rhythm with sounds based around the syllable Tick. I`ve kept that in my head, although I`m terrible at sight reading with that method (I`m just plain terrible at sight reading).
Basically we would end up saying stuff like `"Tick-ah-tick-ah Tick-ah-tee Tick-ah-tee Tah". This is a measure of rhythm in 4/4. The "Tick-ah Tick-ah" is Sixteenth Notes. They have the same length as each "Tick-ah-tee", which are two Sixteenth followed by an Eighth Note (tee). The "Tah" is a full quarter note. I find this faster to pronounce both in my head and with my mouth for some reason. You just accent the syllables for syncopation by changing the tone. For 5 notes per string I would probably say `Tee tick-ah tick-ah Tee tick-ah tick-ah" or "Tick-ah-tee tick-ah Tick-ah-tee ticka", only accenting the first syllable.
Personally, I wish I was good at actually counting! I think that, for me, it would more useful for figuring out Syncopation quickly than it it would be for getting a feel for X notes per string. Counting is great for getting the feel at low tempo but eventually I simply can`t pronounce the numbers at high tempo.
Also, say you are walking down the street and you have a rhythm in your head, or hear a cool rhythm in a song. It is useful to be able to count rhythms while clapping, not just when playing guitar. Even with my guitar teacher rhythm was usually first taught by clapping and later applied to guitar playing.
We never got into 32nd notes, but for quarter notes it was always "One, two, three, four...", for eight notes it was always "One and two and three and four" with each "and" being your off-beat, and for sixteenth notes it was always "One ah and ah two ah and ah three ah and ah four ah and ah" with your "and" remaining as the off beat and the "ah" sounds for the sixteens notes between the eighth notes.