I need help, not you

Based on recent discussions, I' m doing some modeling and supposing, but know jack about aluminum arrows. I know the first two #s and the second two stand for something, but what?

Shooting a hard single cam with a 100 grain tip, easton' s chart recommends 2315 and 2413 for a 27" arrow and 2317 and 2514 for a 28" arrow, all XX78s. Which is the better arrow for each length?

Thanks in advance...