Consider also if you are mostly a cruiser where you want the tack and the clew. Placing the tack as low as possible will obstruct your visibility and probably cause your sail to rub on the bow pulpit and lifelines. Raise it up a bit and you improve visibility forward and avoid the rubbing. Raising the clew will greatly improve visibility as well. What you are trading off here is sail area and potential sailing speed for increased visibility. If you are sailing alone and not racing my suggestion is to opt for more visibility by raising the tack and the clew.