Don't do it! I was raving about the SR-225i and loved them. Made the mistake of getting the 325i and feeling like I lost something. I've been trying to get the 225i again ever since.
I too quickly sold the 225i after thinking the 325is was an upgrade.
I still need to try the 125is.
It seems like with the 325is I gave up some mids for more bass and treble.
That doesn't surprise me. I found the SR325 to be the most V-shaped of the Prestige Series. I actually preferred the SR60 with L-Cush pads to the SR325.
But here's the problem. I never did a more extensive write-up of the series because I started to realize that there's some rather consistent inconsistency among Grado models. That is to say, I have heard two different SR225i's that sounded very different (one had far more bass than the other). I have heard multiple RS1i's that sounded quite different. And if you read through that thread, you'll find absolutely contradictory impressions of the same model headphone between another person and myself. Also, if you do some searching on the forums here, you'll see that I'm not the only one to bring up the issue of product inconsistency.
So what does this mean for us? It means any extensive write-up comparing the entire Prestige Series must be taken with a fistful of salt. And, at that point, it seems almost futile and potentially misleading to publish such a write-up. The best thing a person could do is to audition the entire lineup for themselves...but I know this is not always an option, so things indeed are tricky.
This is why I am a strong proponent of recommending the SR60i to people. Just grab the SR60i and use the L-Cush pads, and be done with it. Most people here will agree that Grado has a "house sound," which just means that the SR60i has a similar sonic signature as the other products in the Prestige Series lineup. The Prestige Series even has the same "house sound" as the Reference Series. Only the PS500 and 1K models depart from this house sound. Obviously you have minor differences between models, but the general Grado signature is always there.
I like what tdockweiler said above. I want everyone to understand what he's trying to communicate. Do not assume that you're getting a better sounding headphone by going up in the Grado lineup! I did this same thing, and in the end I actually "downgraded" in the lineup once I actually compared the entire lineup. I assumed that by going up the Grado lineup, I'd be paying for better sounding headphones. Really the entire Prestige Series sounds about the same, with minor differences here and there. What you enjoy most is more up to preference than to technical improvements.
Audition before you buy!
Edited by Biscuitz - 4/13/13 at 2:38am