Mr Kirk
As backpacker has said what we are looking for is a 3 degree descent path and the three times rule will give you this.
To achive the target altitude at the aircraft's normal decent speed you have to set the correct R.O.D for that speed, I cant see why you seem to have an issue with this.
With piston engine aircraft you should be going down with some power on to avoid shock cooling (check the BGA website for the most in depth reserch on this) and with a jet you will be descending with the throtles shut.
Most piston aircraft will descend at about 5-600ft/min this works for both engine cooling and passenger comfort, with a pressurised jet both of these factors are not an issue normaly.
I went flying twice yesterday and descended both times using the three times rule to descend and both aircraft got to the point in space that I required with little effort on my part. And just in case you are wondering the first sector was on an A320 and the second on a DR400-180 so in practice it works at both ends of the speed range.
I do have to question all those who turn this into a "black art" if they think that it is worth the effort? After all brain power that is being used for this in depth calculation cant be used to check for things like the MSA.