Thanks giloc! It was right below the part I'd read a couple of weeks ago about adding the 50' for altimeter error!
"Pilots with a valid Instrument Meteorological Conditions (IMC) Rating are recommended to add 200 ft to the minimum applicable DH/MDH, but with absolute minima of 500 ft for a precision approach and 600 ft for a non-precision approach."
So the minima are not 500/600 higher for an IMC rated pilot, but absolute minimums to consider after adding 200 feet to the DH/MDH.
Although the AIP says these are recommended figures, only a brave pilot would fly to limits below those recommended for his IMC rating.
Thanks again!