Any thoughts Easton FMJ 6mm 320 spine and Easton FMJ 390 spine Comparison, or On what others use

Hi I own a Halon 6 , with a HHA single pin 55-19. I'm shooting FMJ 6mm 320 28 1/4 '' 70 lb bow maxed out. The 320 are 10.6 grain per inch. I went to buy a half dozen more. They only had the 390 FMJ 6mm. There 9.7 grain per inch 28.1/4. I bought them thinking I will have to re-sight my bow. I was wrong out to 60 yards they fly the same. 3 arrows group about a inch to inch 1 / 2 group.