Doing a side-by-side comparison is tricky because different cans respond to different amps. Some of the Grados are probably easier to drive with relatively weak power (a receiver with a cheapo headphone jack, straight from a computer, portable players). I auditioned the 225 (they didn't have any higher), and I was put off by the discomfort of the pads. They have a distinct sound signature, and some people love 'em, some don't. I didn't.
I ended up with the AKG K701, and I can hear how they would seem subdued from a weak source. You have to turn it up louder. I'm currently researching whether the HK AVR 645 will have a decent headphone amp in 'em, or if I need to get a separate headphone amp. If I were to use them more with players and computers, I'd have opted for the $90 Sony MDR-7506.