Well since STR give chance to double damage is always good but since GH already have a high STR you should be fine just with +WIT, the problem with add STR is that you will have -CON and GH already have low CON.
But is just the player choice, try those setups and see what you like more, but like i said you should be fine just with +WIT.
If you play in PVP servers maybe STR is not a bad idea since all have stuff +++ so extra damage is always nice.