Awesome, thanks for the quick response. The HD600 is quite a bit cheaper than the HE-400, so I think I'll stick with that unless there's a HUGE difference in sound (which I doubt given diminishing returns). I'm curious as to the signature Grado sound, but it's probably not a great idea to start with a high-end one.
Agreed. From what I've read, there's not a big difference between the different SR/MS series models. I'd get the $100 Alessandro MS1 and if you particularly love them then possibly look into the higher end models down the road.
But for your genres and needs I would choose the HD600 or HE400 over any Grados, mostly because of the Grado's lack of a wide soundstage.