To be honest at the time of the cable upgrade I never really noticed a "wow" sonic boost. But what I can say is that when I took them along as a reference pair when I was considering adding to my collection the GS1000 and or the GH1. I walked out with just my RS1i's been disappointed with what I heard from the GS1000/GH1.
The only Grado that even came close in my mind was the PS1000i. If it was not for the price I would have got it.
I even compared it to the RS1e and was surprised by the Superior sound coming out of my headphones. What makes my RS1i stand out for me in the lovely bass I get out of them. In fact I would say it's the best bass I have ever heard on any headphone. I'm obviously no "expert" in the matter, far from it actually, but that's my take on it.