Grado headphones tend to have a sound that you either love or hate. I'm afraid I fall into the latter camp, but I know lots of folks who's opinions I respect that are Grado lovers. So, please take my criticisms with a grain of salt.
To my ears, Grados generally have two faults: the bass lacks authority; and there's a harsh spot in the low-treble around 2kHz. Fortunately, it appears that playing with the pads does indeed effect the sound mildly, and both problems above can be tinkered with.
I'll be mentioning some of the other measurements taken, if you…