To me, soundstage is just an illusion, instrument separation is what is important and you get that with all the aforementioned headphones. I have a preference towards Grado for bright treble and a forward (distinct) midrange because I can listen at lower volumes yet hear the detail.
Sennheisers will take the crown if you want soundstage, I'd be an idiot to tell you Grados even had one, but absolute detail will go to Grado along with treble extension. The treble extension on the lower end models is accompanied with "sparkle" which is a nice way of saying you get a little bit of bzzzz to the treble which can sound pleasing, but on the higher end models the treble will extend even further with increased clarity. On the SR-325 it's really as good as it's going to get, the higher end models I've heard with exception to the elusive PS-1000 add warmth and bass to the sound via their different cups, but the SR-325 is as high as most people will end up going anyway, some prefer the 225, but both are excellent.
I don't even enjoy rock and metal in particular even though with properly produced music of either genre you'd really get 100 percent, but I prefer to listen to orchestral and lead guitar soloists like Yngwie Malmsteen and Paul Gilbert. I hate when people romanticize how headphones sound because after all it's just two drivers but you get an uncanny amount of detail and warmth. For instance Yo Yo Ma I picked up just because... and I believe where the HD600 will do all of it in it's entirety, the Grado SR-225 will do it with tight punchy bass and a very rewarding treble presence. The treble comes off as shrill to some due to it's brightness, I either suffer from extreme deafness at this point (doubt it) or I just became acclimated to the treble coloration.
Honestly it's a win/win/win situation. The HD650 is smooth with a very organic/natural sounding frequency response, yet veiled (treble is forcefully silky, which may cause some purists to dismiss), HD600, neutral, yet some people might not like that, Grado detailed and just plain fun, but some criticize it for being overly bright and quality of build is questionable compared to the others.
If it were me and money wasn't a concern, it'd be a cointoss, it takes a few tries to get your preferred sonic signature down and from there on, you just buy what you can comfortably afford. Nobody said Sennheisers were bad at rock, it just all depends on what. If it's speed metal it's probably not going to fly, but anything with a moderate pace should absolutely sound good through almost any good headphone. A friend recently told me a good headphone plays all things well and isn't genre limited... he also has more money than I do so....
If you ultimately want a well versed opinion, call HeadRoom. They are the ones who convinced me to get the Grados AND the HD580, even though it wasn't from them at the time since the 580 was d/c'ed. Great people.