The Hidden Blade Assassin's Creed in Depth

This video shows several ways to get to the plans and the fastest way I've found to get to blowing up one of the two machine guns. Details are under the 'read-more' link.

50% sync blitz
The 100% sync goal in this mission: don't kill anyone before you destroy the plans. At least, that's how Ezio did it. I'm no guard-loving turtle, though.
This is a fairly straightforward process. While jumping off the cliff, aim to land next to the building. Make sure that the distance between you and the pigeon poop is about one to two feet, which will ensure that you jump in the right direction.
While flying through the air you can select some sort of ranged weapon (D-pad is the fastest way). I select the sword, because my D-pad configuration is the default one. Next, just run, lock on the guard and shoot. Be careful not to let go of the attack button immediately as the lines have become one, because Ezio won't shoot in that case. Running further, you do the same with the second guard and make your way to the plans.

100% sync blitz
Same start as the 50% sync blitz, but this time, there's no need to select a ranged weapon, because we aren't going to kill anyone. In the video, you can see I run really close behind the guard. He won't turn around unless you actually bump into him while doing this. AI fail, really.
When you do this blitz, there's no real need to hurry, because you'll have to wait for the guard next to the plans to get out of your way. Still, it's as fast as can be. (Or at least as far as I've looked.) If you're standing against him when he turns around, he'll notice you and you'll desync.

Ghost run
The goal is simple: don't kill anyone and don't be seen (no yellow bars). This requires a small detour, because jumping down as done in the blitzes gets the guards to notice you. When jumping off the cliff, jump forward, just next to the pigeon poop. (Funny how that differs only one character from 'pigeon coop' ) This will cause Ezio to get pulled to the right and land somewhere on the cart, or, in rather rare cases, next to it. I get off the cart by only holding , to prevent Ezio from jumping. I think this glitch has something to do with the mechanics for a Leap of Faith and the mechanics for landing on beams. For the first part, you're pulled to the right because the LoF mechanics tell Ezio to move to the right in order to land in the haystack. In the second part, the beam mechanics pull Ezio towards the cart. Very interesting, but back to the run.
Running around the corner, make sure that you don't step on the barrels. This will cause you to immediately get on top of the wall, which will lead to the guard spotting you. Doing a wall-run, then climbing up the wall (as shown) will give the guard just enough time to turn around.
After you've gotten around the building, there's a small difference with the 100% sync blitz. You have to jump on the stack of crates, then get down from there holding only . If you don't do this, Ezio will make more noise (groan, whatever), which causes the guard to turn around. You can run straight towards the plans, since the guard guarding them will have just walked by them.

Finishing up
If you look at the weapon icon before and after destroying the plans, you can see that the number of hidden blades changes from two to one. Weird. It's kinda revealing of how little play-testing got done.
After having destroyed the plans, I get on the very edge of the desk, then perform an advanced wall jump (++). This causes solid wall behaviour from the shed, which saves a moment because there is no animation of Ezio swinging. The animation for getting up from hanging against a solid wall also seems shorter. I screwed up a bit on the last part of the roof, but couldn't be bothered to re-run for such a small error. Correct procedure is to either jump a moment later and land on the ground, or to press when on the edge of the roof. I usually do the first, which causes Ezio some damage. In any case, blowing up the first machine gun is very easy after you've come down from the roof. You get plenty of time to escape, so I jump on the dolls for fun. This also shows that you don't need to go through all checkpoints here.

Notes
First, the ensuing chase after the second machine gun escapes, was already shown by Jack, so I stopped recording there.
Second, the guards already start patrolling when the mission has loaded. This means that they are active during the cinematic bit at the beginning of the mission (not shown). Luckily, only the ghost run is affected. You have to wait for the first guard you run past to walk away. He'll take a left turn, after which you can run through without being seen. It's pretty easy.
The guards patrolling during cinematics isn't mission exclusive, so it's something to keep in mind when doing ghost runs.
Third and final, the game is in Dutch. It was the way it came and I haven't found a way to change the settings (I prefer English in games).