I did a bit of comparing of the stock iGrado and a modified pair I bought from Fureshi (quarter-cut pads and new Mogami cable). The stock still sounds pretty good to me for ~$50 headphone. They are a pleasant listen, and especially when amped with the SR-71 had pretty even response--I do not notice an absence of mid-range, for example.
The modded pair certainly has more going for it, and cutting out a quarter-sized hole in the center of the very thick pads makes up a chunk of the difference. The cable requires more current, but I do think it also refines the sound. More sparkle in the highs for sure, and the bass seems to be more controlled. I have not tried putting full pads on the re-cabled pair to assess how much the holes account for the change.
FWIW, I have a relatively large head, and have not had any clamping or tightness issues. For me, Grado did a fine job a making a comfortable and fun alternative to IEMs or the largely crappy street-style options that preceded it. I gave the stock pair to my wife for running because I don't like her so isolated with the IEMs. She loves them and for the first time has found a non-IEM that stays put and produces a sound she likes. She couldn't stand either KSC-35 or KSC-75s, or a couple different bud types either.