Are there any join charts similar to span charts?
For vertical orientation of PT 4x4 you should simply plan to purchase the timbers that will be used as posts full length. So if you need posts 11' 2" then purchase 12'. If you need 14' 8 1/2" then purchase 16'. In fact if you plan your overlengths right you can use the cutoffs for locations where you will need a short piece such as over the door or for lookout blocks.

There are really no real good strategies to splice a vertical post when you can get the material that you need. Spliced posts just cannot take the same lateral stresses that a non-sliced post can withstand. Plus there is the consideration that making splices is a lot of work.