The usual cut-off spot for SOUL LEVEL is around 120, though some people go a tad higher.
For Str and Dex, as well as Int and Faith, it is 40-50. 50 allows you to use 1-2 special items and spells, and is slightly higher than 40. Usually though if you are having trouble fitting around 120, taking 50 points away to 40 is fairly common.
For my int build, I have 50 int so I can use ALL spells, and all my weapons scale off of int so it is useful, plus with 40 end and 40 vit, plus 23 attunement, I don't need points elsewhere...
However, for a faith build, there is only 1 miracle, sunlight spear, that you need 50 faith for. This can be good for PVE bosses, but isn't that great from what I here overall, especially in PVP. In addition weapons that scale with faith, occult and divine, usually are quite inferior to elemental weapons, meaning that 40 faith is just fine most of the time. I have yet to make a faith build, so please correct me if I made a mistake in there... --- You want to know the best leveling spec for warlocks? here it is: http://www.wowhead.com/talent#IrGroGoGcdhbM:RMsVdmmMz