MS-2 and 225 and very different from RS-1 and 325. I prefer the 325s with most pads by the way. Some quick thoughts:
Using bowls:
RS-1s: Muddy everything with ok bass.
SR325: No bass, harsh highs.
I still prefer the 325s here because even though the highs are harsh the level of detail is something else, as the RS-1s are real muddy with bowls imo.
Using reversed bowls:
RS-1: Best pads for the RS-1s. Bass is less harsh than with flats, and everything is in general less muddy than with bowls. The mids especially shine.
SR325: Lack in the bass department. Highs are clear and detailled, mids are fast and dynamic.
These are the only pads where I prefer the RS-1s. The SR325's bass loses its impact with reversed bowls.
Using flats:
RS-1s: HUGE bass. Too huge for me. Its slobbers all over the place but is very deep and has alot of impact. Can be fun. The mids are also pretty great with the flats. Highs however, are muddy.
SR325: Perfect bass. Not as deep or as impacty as the RS-1s, but more controlled and tighter, faster as well. Mids come very close to the RS-1s, lacking only slightly in dynamics, but I really have to concentrate to hear the difference. Highs are awesome here. Straightforward, vibrant, detailled, clear and fast. I've never heard so much details in the music.
Here the SR325s win hands down. Theyre "almost" perfect for my tastes. I think the sr325i will surprise me, and I will probably upgrade to PS-1s in a few years
EDIT: I'll add to this that I have C Pads but only for the comfort factor. IMHO the pads take away the straightforwardness I love with the Grados when listening to music. I use them for movies and the likes. Alot of people will prefer the C Pads sound rather than the original Grado sound though. They do help the bass alot depending on your taste, make them comfortable to wear, and by taking away the "in your face" feeling, makes them more comfortable for long listening sessions. Theyre a must for every Grado owner