Usually climb at least 20 if there isn't a canopy. If there is I just go as high as I can get (I hunt a 25 year old pine plantation so usually 18 to 20 is about as high as I can get before I get to limbs). If it's a nice big old growth, wide, straight pine I go around 30. I've got some old growth pines picked out overlooking clear cuts where I plan on going around 40. I've used my range finder to confirm my 30 foot climbs. I really think going high helps with scent, and I mean a whole lot.

I wouldn't climb that high without a treewalker, though. Those spikes don't let go of the tree without some force. Always make sure to climb nice and slow and deliberate.