The strength of mage's Ice Barrier is solely a function of spellpower. Ice barrier lasts
a full minute..
At the very start of a bg, or when rezzing, you can switch to PVE gear and blow any
on-use trinkets which maximize intellect/spellpower, cast ice barrier, then switch back. This
will get you an ice barrier anywhere between 10-50% stronger than normal.
In close fights, that extra absorbency is quite decisive.
In theory you could build a whole gear set, gemmed and enchanted for int/sp which might
give your barrier a 100%+ resistance. That would make you pretty tough to beat.