The 320i brakes are almost as small as the 125i brakes I believe. I think they are 312mm. Not worth it.
A good budget upgrade is the E90 335i front brakes. The calipers are direct bolt on and then you use a 348mm rotor. The calipers are readily available used for around $100 USD a piece or less.
https://www.1addicts.com/forums/show....php?t=1132152