I'd like to suggest something else to reduce bookkeeping.
Adding bonus Experience Points for a high prime requisite score is pretty standard for older editions, but it had one headache: you had to keep doing math on it. Every time you gained XP, you needed to add 5% or 10%; this required constant rounding (which was inaccurate) or having a decimal point on your XP value (which made it look too picky).
An easier method is to instead
reduce the amount needed to gain a level. That way you're only keeping track of a single change. Lower the goal, instead of raising the reward.
Now, the obvious question: doesn't that mean that characters need
less XP to gain a level than in the original system? Yes, but the difference is pretty slight:
- A fighter with a 5% XP bonus would need 1905 + 95 = 2000 XP. In the other method, he needs 1900 XP.
- A fighter with a 10% XP bonus would need 1819 + 182 = 2001 XP. In the other method, he needs 1800 XP.
This also means that if someone somehow improves their stats and qualifies for a higher XP bonus, you still just change the one value.