I just had spent about 2-3 hours comparing the RS1i and the GS1000i. The longest time i had exclusively with them, of course not having my entire library with me at the time.
I must say that i found the GS1000i probably more worth it than the RS1i, considering the fairly slim price difference. The RS1i, while good, sounded like 'standard', smoothend SR325is or more mature SR80i, incl. intimate / compressed soundstage.
The GS1000i adds air to the Grado equation, making me feel that all the Grados under the GS1000i ( / PS-Series) are mere gradual build-up to the GS1000i.
They are what Grado intended the sound to become at the very end.
It is not perfect, but refined and natural (vs. analytical) as a Grado should be.
Seriously considering picking them up and skipping the other steps. If i do that would be the GS1000e
Yet i feel that they are expensive for the 'simplicity' of the design (vs. HD800, T1, LCD2...). Peace of wood with driver insider and the same gimbals found on the SR60.