I own the GS1000i, I think the V shaped soundstage, need for amp and need for long burn-in makes them more finnicky than other Grados
I think the bottom review isn't bad and better than most I've seen:
http://yklee118.blogspot.com.au/2013/03/the-grado-gs1000i-true-reference.html
Key points for me are that the V shape makes it easier to listen at low levels, the ultra smooth sounds and sheer range make a lot of junk sound amazing, not for dark neutral sennheiser listeners. I prefer the GS1000i's since they not only have the powerful Grado live concert experience, but they're not adjusted for being more palatable or balanced >=] an antique wooden violin isn't as sonically perfect as a metal or digitally created sound but has a live feeling you can't get from others.
The build quality is crazy and no two are the same like all classic Grados of course ^_^
Thanks for listening to my 2 cents