In reply to BolderLicious:
Important as the arm and leg factors are, I would say that even more relevant are:
The Gulp Factor
The Gloom Factor (for climbs like Black Cleft on Cloggy)
and The Sphincter Factor*
*In a similar vein to recommending the necessary breakfasts for a given climb, guidebooks should also indicate the nearest suitable locations for relieving oneself before a climb. The greater the Sphincter Factor, the more necessary this is. With an Extreme Sphincter Factor (also known as a Brown Alert), there is a risk that the location is on the climb itself.