Even daylight balanced fluorescents have the big, sharp mercury ~488 and ~546 nm spikes, which cause problems even if the overall colour temp is 5000K. Those spikes can wreak havoc on the white balance.
By and large, 400x really likes ~5000K light. If you are really concerned about colour fidelity and have mixed lighting, 400x is simply not the way to go. And neither is velvia or provia or even astia (although astia does fare quite a bit better in mixed light).