Honestly, glass is glass and OEM or Pilkington it wouldn't bother me in the slightest. Anything is better than glass with a dirty great crack through it!
I've never specified OEM glass when having it changed. Granted that was only in the MR2 (didn't know better), VXR220 (likewise but was very careful with the fitting by AG) and the MX5 (too cheap to worry about). I wouldn't care about OEM glass on the BMW, it's 13 years old so anything will do.