i think grados sound great with classical music, especially with smaller ensembles. some may not like them for classical, and that's fine, you should consider that input. however, the grado=rock and senn=classical 'rules' some people might be tempted to parrot based on what they think the consensus is is way too arbitrary IMO. grado's are extremely capable with stringed instruments, and this certainly includes cellos etc. if you've listened to the grados and are truly that attracted to them, go ahead and get a pair.
with regards to the 325i vs 225, i listened to both and chose the 325i. i found the 325i to be slightly more capable at both ends (high and low frequencies), but the difference is pretty small. in some recordings I find the 325i's to be too bright, but this really isn't an issue in classical recordings for me. mostly loud rock with high-pitched distortion, guitars, cymbal crashes. but i think the 225 would probably have the same problem in that regard too. while the 325i's might be a little brighter, irritatingly bright is just the grado sound at higher volume.
i will say for classical i personally am preferring the hd-650's