I would like to preface this by saying this tactica isn't for everyone. In fact Most of you will math hammer this until it makes zero sense and only a madboy would ever try. Well let me tell you that its the intangibles that make up the math and that just because he's a crazy madboy doesn't mean he's dumb.
This tactica will include 3 options I have used in the past to handle the bane of orks, the template. More over, tanks at a range. One that is more familiar to everyone will be the Green Baron. The next will be a little less common, and that is the use of Snikrot and his kommando elite. Finally we have an even more obscure and wildly crazier option of attacking with Boss Zags.
Option 1 is a staple of most ork armies as it is cheap, very effective, and uses a organization slot that doesn't get a lot of use in the ork lists. Ironic that fast attack plays little in a Kult of speed list but I digress. The green baron for those that do not know is not an IC, but rather a squad of one single defkopta rigged with rokkits and a buzzsaw. The rokkits are a twin linked high strength assualt weapon, and the with multiple attacks at an above average strength on the assault it makes the Green Baron relatively effective as a unit to take on light armored vehicles.
The green baron is also extremely versitle in it's deployment. It has scout, so it may make a move after deployment. It can turbo boost during it's scout move for a nice save and if you are lucky enough to go first, can normally reach a vehicle on turn one after boosting during the the scout move. Since you get rear armor in assault, it makes vindicator tanks and dakka predators much easier to handle.
The other option for the Green Baron is his ability to come in from reserves from the side of the board. Hopefully getting the side his tank is on, and destroying it the turn it comes into play.
Normally I would start him in play and send him on turn one as I don't have to worry about rolling for reserve, or rolling to come in on the wrong side. But something to think about and depending on your oponent he "should" think about is that your green baron "could" wreck his tank at the onset of any of your turns. Therefore he will keep it mobile so that your baron doesn't autohit in CC. This helps you by preventing him from being stationionary gun platform. Dakka preds can shred a boyz unit in a turn or two, but if he can only fire one weapon option from moving, all those boyz saved is worth the price of one Green Baron even if he doesn't destroy the tank.
The next option for ranged tank removal is Snikrot. Kommandos are sneaky viscious totally orky vandals. Just mentioning Boss Snikrot brings sighs and moans of utter disgust from almost every opponent who has faced him before. When he comes in from reserve, his unit of Kommandos picks which side the will be coming in from.
After letting that last sentence sink in, I will say that I am not going over the glorious tactic of having two burnas in a kommando squad show up and the chaos they can cause to infantry. But, Snikrot himself is where it is at. I run him in miniature suicide squads.
His medium high strength on the charge with his large amount of attacks that reroll to hit are definately a threat to any vehicle that likes to sit back and pound the ork lines. Having him in reserve almost garrantees that your opponent will move his units at least 12" forward to stay out of his assault range from the table edges. If he doesn't then Old Snikky can go to work on whatever he has neglected to bring forward with extreme prejudice. If he does move them all forward which will happen more often than not, it means that all his units are closer to the rest of your boyz that are running towards them from the other edge. It's win win.
The third and in my oppinion most devastating option is the Death from above option. Boss Zagstruck is a nob upgrade for a storm boy unit that lets them assault after the deepstrike. All at the cost of a few of his own storm boyz. WARNING: The following sentence is opinion! Boss Zagstruck is my favorite unit in the ork codex.
Space Marines use drop pods to get there vets right behind vehicles to melta thier rear armor. It's expensive and at 2 kill points total for a squad and a drop pod not really worth it. But, If you use Zags, it's one unit. One unit that can drop in, hit with a very high str attack and go out with a blaze of glory.
Just like Snikky, I run zags in a minimal squad of storm boyz. He's almost always assaulting vehicles and storm boyz just aren't cost effective enough for me to try and glance them to death.
Now therre are several drawbacks to Suicide Zags units. Deepstrike can place you out of assault range. If it does, try to get into cover or assault whatever you can. He still gets his powerklaw at a higher initiative so he'll go down swinging. Zags only gets his pk on the charge. Well, Lets face it, at minimal squads, if at first you don't succeed it's there fault at that point you are still alive.
When comparing the three options I have above, it's important to look at your overall army theme and construction before deciding that a suicide unit is in order. Although Snikrot can alter how another player plays his army, his kommandos take up an important Elite spot in your force organization that you might need for burnas, nobz, ect. Both Zags and the Green Baron are Fast Attack, but if you are a kult of speed player you may have several rokkit buggies already selected, or biker boyz.
Do you play with a lot of terrain on the board? If so deep strike mishaps may be more of a threat to Boss Zags. No single option above is a must have or an "I win" button, but they are options for ranged anti tank removal that your opponents might not be accustomed to seeing from ork players.
Remember it's the intangibles that make up the points. You may lose a 150+ points and a kill point, but if you can force your opponent to play to your strengths as Snikrot does, or force them to stay mobile like the barons do you are limiting the functionality of thier tanks and for every turn you limit them you are saving countless boyz on the other end. I know it's bad math to count "possible boyz saved" as points to consider, but if you have had one round where a dakka pred's heavy bolters and autocannon have sundered a boyz squad or a killa kan mob to death then you know that keeping it to firing one weapon or better yet only firing one turn is your best bet.