If you've found your way to this point, you'd probably be interested in Andrew's New Ogre Page.
First of all, I take a totally different tack with Mark IIIs and Mark Vs...
If your opponent is not inclined to fire at missiles, save them, at least at first. They are ideal for taking out howitzers, obviously, but even more important they shorten the game by two critical turns, assuming that your at M2 and minus your main battery by the time you get to the far end of the board. Your opponent will thus have to target them later in the game, when he has fewer units, and when he desperately needs those tread attacks.
If you don't know whether your opponent fires at missiles or not, there's a meta-game gambit that can counterbalance this. Save your missiles. If he doesn't fire at them, save them for the endgame. If he starts shooting at them and misses, fire them at armor units the next turns. If he takes them both out shake your head and say, "you're not going to slow me down in time..." The first couple of turns as the defense are scary; make the most of it.
Ignore the missiles, take your lumps if it fires them. You'll probably only lose one unit, and it would take six unit-attacks to get rid of both of them. Kill the main, and then hit the treads until the Ogre is at M2. You should get it down to M2 early enough that you can evaluate whether to kill the missiles or go for M1 next. If you don't get it down to M2 before it hits the last third of the board, its all over anyway, missiles or not.
If you've got the Ogre down to M2 and it has to go under a HWZ to get to the CP, focus everything on the missiles and let the HWZs (you do have more than one, don't you?) do the rest. Otherwise I would go after M1 first, then hit the missiles. The missiles extend the Ogre's range from two to five (I'm assuming you're not wasting attacks on the secondaries), but M2 increases the Ogre's range by one *per* *turn*. You have to kill the treads eventually anyway, or it won't matter what weapons are left.
So go for M1 first, then count the hexes and the tread units. You're fifteen tread units away from a win, and since each tread attack has a one third chance of success and success is subtracting the attack's strenght from remaining treads, can you bring forty five attack points to bear before it gets to five hexes range from the CP?
A Two to-One attack has a fifty-fifty chance of taking out an Ogre weapon, whereas two One-to-Ones have a 56% of destroying it, with an 11% chance of hitting two things (44% NE, 44% NE/X, 11% X/X!). So stick with One-to-Ones. Probabilistically, you need three to kill a missile, *six* to get two. Those same six three-point attacks would take out six tread points (probabalistically), but they buy you three turns, since they shorten the Ogres destrucive range from give hexes to two (you've killed the Main Battery or you're in deep trouble), and that buys you three turns (the Ogre is at M1, or again, you're in deep trouble). Actually, you probably only have six armor units left, if you're lucky, so six attacks to kill the missiles is going to take you a whole turn, so this only buys you two turns.
So do that if you need the two turns, but there's one other factor to consider before ignoring them if you think you can get to M0 before five hexes of range. Do you have only four or five armor units? You're not targetting the APs, I hope, so you Infantry has probably been whittled to nothing, or one platoon. What would happen if the Ogre fired those missiles at armor units, possibly combining this with a reverse charge to apply the secondaries to the armor as well? Sound like a dumb thing to do at M1? It doesn't matter how slow the Ogre is if there are no defenders left. If he can get you down to two GEVs they would require ten or eleven turns to wear the Ogre down from 14 tread units to zero. Two Infantry platoons could shorten this to nine turns (they don't survive like GEVs), but the Ogre probably is not that far away from secondary range. So if your remaining defense is fragile this way, you might kill the missiles to make sure the tactical situation doesn't change to suddenly.
This situation is different because you have a lot more missiles. On a Mark III the amount of firepower required to take out all the missiles is 60% the firepower required to reduce movement by one. On a Mark V it takes 90%. While the defense has increased 80% in armor and 50% in infantry, the Main Batteries are up 100% and the missiles are up 200%! (I hate % terminology, up 200% = tripled?) So the game is very different.
The missiles range and strength combined with quantity can create *very* sudden changes in the tactical situation when the missiles are used all at once. If the defense is GEV-heavy you can eliminate one third of the defenders in a turn, and your opponenet will suddenly be placed outside of his original plans. You can also move to one side of the board and clear it out with missiles and guns, giving yourself a turn of breathing space as the defenders run to catch up with you.
With eighteen armor units available the Defender is more likely to splurge on two, three, or four howitzers. I would save the missiles for these, but if your opponent starts shooting at them (a clever move to maximize on his investment in the HWZs) you should try to eliminate some armor with them.
Probably the best thing about the Mark V is that you can fire two or three of the missiles and take out an armor unit or two, and make your opponent think you're going to use them up, and with relief he decides he won't have to worry about them in the endgame. But then you save the other three and when you're down to M1 they give you the equivelent of three extra turns of movement. But then, they only take half as much work to eliminate.
All the statistics above are the bad news. The good news is that your real enemy is tread points, and tread points are only up 33%. But then, the worse news is that the map is 0% longer.
So I still say kill the Mains, take your lumps from the missiles, get behind the Ogre and shoot the treads. It takes as much firepower to eliminate all the missiles as to take out eighteen point, and you *must* shoot all the tread points to survive. The missiles are likely going to take out five armor units, but maybe less.
The only time I'd start shooting at a Mark V's missiles is if it had just one or two and was about to enter missile range. Do a range-time calculation considering one missile to be as tough to destroy as three tread points, but remember its only destroying the *last* missile that shortens the Ogre's range from five to two.
I'm hoping all this will generate some discussion, and I look forward to seeing it.