The original PS500 is the polar opposite to the RS2e. Now I didn't own the PS500e and RS2e at the same time like I did with the original PS500 so from memory I would say the "e" series have more in common with each other than they differ (the land of settle differences). The PS500e had more bass where the RS2e has less but tighter and more controlled. Also with the all mahogany cups of the RS2e that produces this tone that sounds so good and natural; I don't know, it's hard to explain. Sorry I can't be much help on this, maybe someone else has had the chance to compare them directly.
Well I only ask because I'm thinking about getting another pair of Grados soon. I got the GH-1 this week and I've tried out the RS1i. I'm chasing the sound of the PS1000s, but their price tag is out of range at the moment. I'm shopping for opinions around here because they're folks who've said the GH-1 with the G-cush is very comparable, as is the PS500 with the G-cush. From what you mentioned on the RS2e, I'm surprised to hear it's not at all like the GH-1. To my ears, the bass is clear and controlled but it is not tight or wound or rumble-y and bloated. I'm working on posting my impressions of them, so there will be more later.