40 attack, 85+ strength, 1 or 40 defense, 85+ ranged and 1 prayer.
Some people opt for 65 dung for Gravite 2h, but it's not practical for pkers who don't want defense experience.
If you range with rapid arrows (range/2h is one of the most lethal pking methods in f2p), switching to Gravite 2h doesn't switch you to the right aggressive style that uses smash or whatever the Gravite 2h has a high attack bonus in. If you were to manually switch, switching back to the maple shortbow would put you in the longrange style which gains defense xp. Overall, Gravite 2hing tends to be tricky and really isn't worth it unless you use it as a primary weapon.