FWIW - the stance on a 325 is never the same as a 318iS due to the weight difference
I have ridden in 325iS and 318i m10 with J stockers. It's definitely a case of preference. A lot of people say they don't care about ride comfort but it's a relative statement as it comes down to how many miles you drive, the quality of the roads, the dental plan you're on and if you have any gf/wife who rides in the car with you occasionally.
Stiffer isn't always better. Will you be autocrossing or doing HPDEs?