In a way it depends on how quickly and painlessly you can hand them in. Obviously you don't want to overstrain your body to make xp, and likewise you don't want to waste time if you are really slow at clicking about.
Every 4 bone chips give around 7777 xp. Going by
the wiki it takes about 1,500,000 xp to go from level 6 to level 12.
5 backpacks of bonechips will take you from 6 to level 12.