If you're fighting with him, on Attack, then it'll be nice to have, but not amazing:
That's 859/tick.
Of course, the real question is how it looks on Defense…
In BGs, a standard +100% attack will mean that the Attacker suffers 41,220 Coldsnap damage in twelve seconds, if they can't get rid of it, or don't have immunity/Energy Resistance.
In War, defending a node that gives +300% Attack, you'd be looking at 82,440 damage...
Oops. Stupid forums.
Did not intend to post that, twice…