The previous tables cover the abilities and stats that are more or less shared between all the classes. These next two tables focus on the specialized abilities, skills, and talents that can help make a class unique.
Table 9 has the special abilities and skills that even humans can master. I tend to think of these as teachable skills. Table 10 on the other hand is for all the abilities that require non-human physiology or heritage. Wings, gills, and eyes that see infrared are all definitely "beyond human".
Between those two extremes is a whole host of natural talents and innate magical abilities. I'll leave it up to the individual DMs to decide which abilities their human classes can use. Different campaign settings are going to put different limits on human potential. You might give humans access to psychic talents and innate magic abilities, or reserve those for non-humans only. If human clerics have the Turn Undead ability, can other human classes channel different supernatural forces; talking to spirits, summoning djinn, or making infernal pacts? Different worlds are going to play by different rules. It's really up to you to draw the dividing line between human and non-human abilities.
Table 9: Extras
Open Locks - +10%
Remove Traps - +10%
Pick Pockets - +10%
Move Silently - +10%
Climb Sheer Surfaces - +10%
Hide in Shadows - +10%
Hear Noise - +10%
Backstab - +10%
Student of Linguistics - +20%
(Read Languages 80% at L4 & Arcane Scroll use 10% failure at L9)
Turn Undead - +20%
Magic Research at L9: create spells, scrolls, and items - +25%
The only abilities I have listed in Table 9 are the ones already used by the human classes in B/X. I'm sure to make additions, but for now I want this table to just be bare bones so that I can use it as a template for almost any setting.
The costs here are all highly subjective, so feel free to ignore my numbers and make up whatever costs seem fair to you. Even if you want to keep the B/X xp tables unchanged, you could raise Backstab and Climb Sheer Surfaces to 15%, and lower Move Silently and Hear Noise down to 5%. Trading percentage points between Turn Undead and the Cleric Spell Progression is really easy, same with Magic Research and Magic User Spell Progression (but that applies to the Elf class too).
If you want some rough guidelines...
When making new abilities, I usually try to imagine what level of spell could create that same effect, then I set the cost at around 15% per spell level. If the effectiveness of the ability is scaling based on character level (like thief skills and turn undead) or it doesn't start until the character reaches 4th level, I reduce that cost to about 1/2. If the ability isn't gained until level 9, I reduce the cost to 1/4.
Good luck, and have fun!