You pose an interesting list. While I have no experience facing super heavy tanks like the Kill Bursta or Knight Class Titans, I am a fairly experienced ork player and can see the weak points in your army. I see from your other posts that you are not looking for advice to tweak your list, so I will try keep the responses to your questions.
How would I win? With taking more than half of your entire army on 5 heavy units, I would definitely use finesse and speed to beat this army. The dreads acting as body guards for the knight can be completely ignored until after the super heavy tank and knight are taken care of. The dreads are only a threat in close combat and your two monster units would only be engaged during the shooting phase. If I was using eldar, fire dragons in falcons using a cloudstrike formation to deepstrike them would make short work of them and have very little fear of reprisal. The dreads could try and assault them after, but I'd have a pretty good chance of getting off some overwatch shots that would most likely take out a dread or two. Conversely if allied with Dark Eldar, I could take an archon with a webway portal and deepstrike wraithguard or fire dragons and D weapon or melta them to oblivion. These options would cost roughly the same points as the tank and knight they were taking out and are pretty much guaranteed to strike first with little fear of reprisal. That would leave half your army to have to face what remained of mine. Granted, you will have a turn or two to use their shooting attacks to whittle down my forces, but if I reserve most of the army, except for some rangers, maybe take a voidshield generator and take an autarch to guarantee reserves, I'd still have half my list to deal with some boyz in ork trukks and a few koptas. Take a unit of dark reapers and they'll easily deal with the koptas. Scatterlaser jetbikes or dire avengers would deal with the few small units of boyz. These units would easily win on maelstorm points as well.
With Chaos Marines I would have a harder time, but not impossible. Deep striking terminators and obliterators with melta/plasma would do well against the super heavy and knight, with again, little fear of reprisal. Combine these with further fire support from havoc squads with lascannons, chaos bikers wielding melta/plasma. Take these guys with marks of nurgle and they would do well against the remaining ork boyz as well. Just taking a single combined armed detachment I could take up to 9 obliterators, which is only 2/3 of the points that the tank and knight are. Again they will strike first when deepstriking. Fill the rest of the points with nurgle bikers, nurgle marines, add a sorcerer for some psychic support and it would work nicely. Hold stuff in reserve and keep the rest of the army that started on the board well away from the knight and super heavy and sit and wait for the obliterators to show up.
Would I have to tailor the list? Only in that it would need to be a list tailored to play against someone playing knights and super heavies. I don't typically play tournament level where one would expect these units. A tournament player would have no issue dealing with using their typical list, as they expect to face knights and the like in today's scene. There would be zero chance that any of my casual lists would have much of a chance against this list, but my casual lists do not play against super heavies and knights. It kind of defeats the purpose of being casual. The eldar list is further away from my normal casual list, but my chaos list would not be far off.
What would be most challenging? The super heavy tank and knight, but they can be easily countered with non-super heavy/non-knight options when they don't have complimentary supporting units.
How would I rate myself? That's a tough one. With Cavalier, Wyddr, and Killersquid rating themselves a 7 in your previous posts, I'd have to give myself a 4 or 5. I've been playing since rogue trader days, but I'm not one for the tournament scene and have never played competitively.
I would absolutely love to work on tweaking this list with you and point out the strengths and weaknesses, to help see if we could develop either a better casual list or a better tournament list. Right now I see the making of two great lists that have been torn in two and combined to make a list that just doesn't seem to mesh with each other. Let me know if you want to go down that route. You have an interesting concept with allying with a renegade knight that I've been toying with myself conceptually for a while.