Ok Muck, here goes... a bit general for the "step by step" you requested. I love the pony and do have success in it but of course there are others who have their own ways(and probably do!) and will probably claim I suck, or they are better.. blah blah blah. Here's me:
Let's assume both niki pilots are reasonabley experienced.
The nikis are at 10k, you are at 15k and all planes are at cruise speed. A quick check of the skies around you and dar shows you have plenty of time(per your description). Perfect!!
As someone said... you really don't need all that alt.. why?
Well, if you dive too fast, you'll lose some manueverability plus if you go too low after your attack, you may give your niki friends shot opportunites on the way back up.
So, first things first. Get them engaged!! Make a pass or two on them so they don't split, break and run in different directions. 99% of the time if you engage one, the other will stick around to "help".
On the first pass or two you will learn tons. Are they left handed? Right handed? Oddly, most people tend to break the same way almost every time. This will be important to note as you will learn.
OK, during the first couple of passes, you're really just gathering info. Don't dive down too fast, use throttle to keep the pony in her sweet spot. Don't single out a target between the two. Their actions will tell you who you should be aiming for.(look for the gross mistake, recognize those and you're set) As you dive in, these first couple runs, take a shot if they give you one that does not require heavy G's to acquire. Make mental notes of their evasive habits.
Ok let's take a paragraph and talk about the rope. Remember, this is my opinion so others may tell you I'm full of crap. Ok with your 5k alt advantage, you really have way more E than you need. And, if you zoom so far up that the niks feel they have no chance to get to you, they may break and run. The thing here to do is keep the horded E you need, but don't let the niks know you are banking it. Steve, how do I do this? I'm glad you asked! Welcome, my friend, to my world. The answer sounds simple. It is sooooo effective that I use it every day: spiral climb.
Think of the spiral climb as a spring. The more it is compressed, the tighter the coils and less vertical it travels. As the spring is relaxed, the coils aren't so tight but they travel more vertically. If that spring were to be straightened out, imagine how long (energy!) it would be. Whether loose, tight, or in a straight line the spring coils are the same length.
Ok, so as you zoom back up, you do so in a spiral over the niks. Why? A couple of really good reasons. As you spiral as opposed to going straight up, you stay in close enough contact w/ the niks that you will keep them interested AND if they decide to cut and run, you are so close that you can quickly snap over and run them down. Also, a spiral rope really allows you to look around and make sure your enemy doesn't have help coming. As you spiral back up, take a good look around to keep your SA in order. I like to stay so close that my victims are actually trying for a shot. Why? Well, let's say I'm spiralling over your niks at say 800-1200 yards(even less if I am fast). These guys are going to be pulling lead like mad to try for a shot(burning more E than you in the process). As they pull, tighten your spiral enough to keep in front of their gun solution. Now you've got slow victims and you can pick your time to roll over and pop them!
Steve, how do I know when? Good question!!! Here is another part of good roping that takes practice. If you wait until your opponent goes nose down you may give him time(it only takes a second or two) to build enough E to perform an evasive. If your opponent just plain stalls this is not a problem but most pilots will nose down prior to stall. The trick is, to learn to nose down into your opponent at the right moment so that if he goes nose down he gives you a sweet canopy shot, if he rolls over you have a nice fat belly shot, and if he feels he is forced to stay nose up, his nose will drop enough that you can rake his canopy/tail section w/out giving him a gun solution. If you go down too early, no problem. Nose back up(to avoid the HO), and start over, or, what I like to do for a change up: Nose up, let him think you are repeating rope, instead do a sort of high yoyo and drop right back down on his now helpless plane.
Steve, this is all fine but there are two niks!!!
No problem, in fact I use this to my advantage.(explained later) Every once in a while, chances are that one of the niks is going to slip off and try to grab to get over you/coalt. Keep an eye on them and make a pass at the grabber to force him into an E bleeding evasive. I call this corralling. It works, Muck, I love spiralling over 6 or so bad guys, watching for the gross error that signals to me who dies first.
Ok you've made a pass or two and you have noticed that one nik tends to break to the right but his break is a bit lazy and you think if you pull G's, you can snap him. Up in your spiral, go thru the coil until you've got the niks in spots under you where you can make a pass on one without giving a gun solution to the other(another advantage over the straight ropes, which tend to clump enemies right on top of each other). Roll over on your victim.... but cheat a little. You know that he is probably going to go right....cheat some in that direction, not enough to be obvious, just enough that you will not have to pull lead nearly as hard to get your gun solution.
I hope you are starting to get the picture.
Ok here's another and my favorite. Up in your spiral, come down on the same guy twice in a row. If he makes a gross mistake, take the shot. Not to worry if he doesn't. Now, after you've made a couple passes, you go back into your spiral. Line the niks up so that they are close to each other but not exactly in line with you. Dive back down on the same guy you've been running at. Instead of trying for a gun solution on this guy, switch at the last second to the other nik. You'd be amazed at how often this catches them off guard! Imagine how well this works w/ 4 or 5 guys under you.
Ok, this gererally covers how I'd approach these two bandits, does it help?
There are other things involved I didn't discuss for now(some: flaps, rudder to bleed E and snap, how you can stall a pony over on it's back and the nose will fall down perfectly, even at full throttle.. etc etc) but I hope this is close to what you were looking for. A good start at least.