oooh, you did it. one of my pet peeves. here we go.
1. the 1/f-length rule is wrong
2. sr effectivness depends on the user too.
i shot at 85mm with my k20 and got sharp pictures well bellow that (more like 1/8). it is not easy, because my 85mm is 1.4 so rather heavy, so there was a difference to my zenitar
. anyway, keep in mind that, according to that rule of thumb (which is wrong), 85mm on aps-c would mean 1/125 or so, so you're getting two stops already according to that, it's arguable how sharp you will get at that speed, without sr, in the same conditions, though (and that is important)
now why is the rule "wrong" (and this is arguable, make no mistake). if you shoot the same subject, from the same distance, and only swap the lens, it is quite valid, but than again, if you do that you're not using the lens right. the logical way to use a lens is imho this way: look at the scene, decide what kind of perspective you want (imagine the shot in your mind, frame it, etc), based on this chose the distance you need to shoot from (which determines the perspective, yes, the distance _alone_ does), and last chose your focal length that will give you the right framing. if you just stand still and swap lenses, what's the point? you will only have one focal length which gives you what you _want_ from you standing position, if you're lucky that is, so all the other shots are mistakes, for the lack of a better word.
how does this relate? well, if you think about it, it's hard to determine effectivness of sr if you don't take this into account. the distance to your subject is _essential_ for the shutter speed you can handhold. try this experiment, if possible with a constant aperture zoom lens: chose a framing, and a very confortable position for you to shoot/handhold, frame with the wide end, see how low can you go (shutter), now zoom in, but frame the same way (so you will have to step back, and your perspective will change), see how low you can go. you might be surprised
.
imho, and based on my own experiments, there's hardly any practical use for the 1/f-length rule, it is rather more like, the photographer has his own lowest shutter speed he can handhold with a certain kit (depends on weigth, balance on the body, etc, so it does depend on the lens), if it's a zoom, it will be the same for the entire range of that zoom, for the typical subject that photographer shoots with that zoom (read: focus distance)
hope this helps somewhat, though it doesn't answer your question directly (didn't own a k-7, sorry, and the k-5 is too new to me to compare to the k20, but i'm quite happy with the later)