Yes the longer the better but when you reverse mount the hood on the lens for storage you don't want the hood to be longer than the lens.
Also the larger the aperture the larger the opening of the hood must be, it's the same that the elements in the lens or larger as well.
It's explained on the toothwalker page.

Indeed you're right about the 50-135 hood ^^

You often see telescopic hoods, you might want to use one of those to get the most effective hood. Simply slide back till it doesn't vignette.
Hama has some for example link

From what I understand the recoil is actually more because the shutter is heavier.

I'm still playing with the thought off an dictated SLR APS-C mount instead of the k-mount. I would most likely buy such a camera if Pentax would come with a good adaptor and with the promise of DA* like lenses for it and an advance body.

Went for other, I simply want better AF.

What I also want to see is the ability to control dictated flash wireless from the camera body.
Also don't forget AF with video please

DAL version is optically the same but you won't have a Metal lens mount, quick-shift focusing and it comes without a hood. If you want a hood and have original pentax I would go for the DA instead because the original hood isn't so cheap.

85mm shouldn't work to begin with, that will vignette most likely. Also as you said lens hoods have different sizes, you've long and short 85mm lens hoods.
The longer the lenshood the more effective they will be.

The hood of the 50-135 is probably so big because it should also be effective at 135mm and also the lens itself is quite long so if you reverse the hood it isn't longer then the lens. That's why the hood of the DA55 is shorter because the lens is shorter.

No it doesn't but hardly any comments about images are given here to begin with (which is a shame), most of the time it's about the subject matter or any other problems that arise.

Does the front element turn? besides that I don't think you have flower screw-in hoods to begin with only circular hoods.
I think you can just take the 1.5X crop rule into account, so you should be looking for a hood for a 75mm lens. Don't hang me on it though.

That's the problem, there is a filter infront of the sensor to protect it also LCD stand for liquid crystal display and there is nothing liquid about sensor so you will damage them when trying to rub them.

That still isn't a rule though and I'm actually looking when this was introduced because with the first competition this doesn't seem to matter, what has changed?

Everything you might want to know about lens hoods link

As you can read the flowerhood match what the sensor sees so if you don't mount it right the hood will get in the photo.

They use round hoods instead of petal hoods with long lenses because a petal hood will be very long.