I fully agree with your maths. My basic assumptions were different though: If players are able to spend MP to max their worship rolls, so are NPC, and they have at least 3 rolls per year (high holy day, sacred time + 1 other, like after or before a raid). On those 3 rolls, a 15 POW char has (21-15)x5=30% chance of increase, or more precisely 65.7% of an increase. In 10 years, that means 6.5 points of POW. If you do the math starting from 11, probability are 88%, 84%, 79%, 73%, 66%, 58%, 49%, 39%, 27%, 14% of gain. That makes a probability of 28% of gaining 5 POW in 5 years, and 63% of gaining 5 POW in 10 years. If you spend the POW to acquire the RP at the beginning, the rate is even faster. This is why I spoke of 5 RP in 10 years: The probability is around 75% to occur.