All Grado headphones use the same driver. I know Grado themselves have denied this, but I don't care... never trust the company who is selling a product to admit something negative about their products; they will lie through their teeth. The FACT is that if you look at the frequency response graphs for the cheapest 60i and the 10X more expensive RS1i, they both are mostly identical! Grado changes the enclosure a bit and makes some other small adjustments (like an 8-conducted cable vs 4, and a less ****ty fake leather headband) but other than that they are the same damn thing. The changes in casing etc do make a (very) small difference, but not even necessarily for the better.
Take a look at the photos posted of the Grado factory where these headphones are made; they are assembled by hung over minimal wage workers who don't care about the quality of their work, and the products are held together by friction and glue! As far as I am aware, the only reason why these headphones are so highly regarded on this site is because they are unpopular and people who waste a tonne of time and money on a hobby don't like coming to the conclusion that the Sennheiser can their friend bought at random for $100 is actually the best deal out there. It would mean they've done all that research for nothing.
Before you say I'm speaking about something that I am not qualified to comment about, I DO own the Grado 325is headphones and I have listened to the 60i later on and could not tell the difference. The 60i is not a bad deal as THE Grado headphone is worth $70... it just isn't worth $700!