Macro Lens Choices
what are you planned subjects? if your subjects are things that move on their own power, like insects, etc., you may want more working distance (distance between plane of sensor and your subject, taking into account the minimum focus distance you need to get to the 1:1 macro ratio). the shorter the focal length, the shorter the working distance as a general rule. if you have to get too close to the bugs, they may move away or worse yet, bite! also, having to get in too close to get to 1:1 limits your light as you may end up blocking it by being so close. so the 40 may not give you enough working distance. nor might the 60. most folks that shoot bugs like the longer focal lengths, like the other poster at 105, or even longer. conversely if you are shooting still life, either the 40 or the 60 may work depending on your lighting options.
depending on your budget, consider the Tamron 90 or the Tokina 100mm macros.
another way to go, since you recognize that you are going to do most of your macro work on a tripod, is an older Nikon micro lens, even the manual focus lenses.