The European ROM was intentionally left mostly unmodified for people that like a stock style experiance. v1.0 of the Euro ROM is just a pre-rooted stock ROM. In v1.5 he added and updated some apps but there's nothing there that isn't already in the Chinese based ROM. His post lists the changes between v1 and v1.5.
Personally I use the Euro v1.5 ROM, I like the small changes he made. I did try the latest Chinese based ROM but there was an aggressive memory saver thing installed on it, I felt like it was interfering with some of my apps but I was never really sure.
Also, I've never heard of anyone needing to do a battery calibration after flashing a ROM so don't think it's needed. FYI: I remember one of the kernel devs on XDA was saying that most people's problems with the battery meter is because Samsung uses a poor method for calculating the battery percentage and that sometimes it gets stuck.