The phrase I like to use is that 'the HD650's can do detail as well'. But for me, the 'rock' music I played through the 325's were so unbearably overpowered by the guitars, that I found myself reaching for the HD's. My friend tried to explain that the 325's are an 'instrumental' ... headphones, but none of the instruments in rock were allowed to come through; such is the brutality of the emphasis on the guitars in particular. Vocals are so far down the 325's list of priorities, it would seem.
O.K. they did well with classical, and if there was a genre for the 325's it would be classical, but as far as rock, pop or anything else goes, I have to say I’m still on the 'disappointed' side of the Grado fence.
I love my iGrado's, my SR60's and the Alessandro MS-1's, but the 325's i'm still having problems with. As for the HD650's it's a matter of having it when you want it. The HD650 can do detail, but when you want a fuller spectrum, they can do that as well. Whereas with the Grado's, when you want somehting a bit fuller, you'll come up wanting. Detail, sure, but i still find the SR325's (325i in my case) one dimentional.
The 650's are a 'Jack' of all trades, but the 325's are 'Master' of one. Problem is i don't listen to just one genre of music!
The other consideration is that the HD's need a good amp. The 325's could get along fine with a CMoy or Fiio E5 (i've lost mine) or something like that. plugged straight into my iMac, bar a lack of real volume the 325's perform well. The HD650 won't let you get away with such a thrifty approach.