Don, I've never seen nuetral current above line current in any of our data centers. Harmonics coming off most quality UPSs, VFDs and computer power supplies are filtered down so that they're really not an issue at all. Heck, a lot of them are simply straight delta and don't even have a neutral connection.
OTOH, I've heard stories from the old timers about a fractional neutral in an old buildings quite literally glowing cherry red from the harmonics...
Based on our load profile, I always specify 100% neutral.
