I'm almost positive it's a -5% penalty for 3.0.3. I am not certain how non-Blizzard sites update their data and we don't fact check them.
We've also been discussing just getting rid of the penalty completely (though this will not be in for 3.0.3, if in fact we do it at all). At 5% it just feels like a dumb penalty, not something you really have to itemize around. This would make Titan's Grip the most overpowered talent in the history of WoW, and doubtless we would be for years having to deal with community questions about how none of their talents provide the 20% dps increase (or whatever it turns out to be) of TG.