Hi Mascott,
I can't give a definite answer as to whether or not it would be safe to run with the cores unlocked but that seems a pretty big jump in Wattage to me and is probably why the cores were locked off by AMD. Personally, if I were in your position, I would O/C with just the 4 cores as this will be the safer option.
Not sure if you can disable either of the extra cores, as I have never played with this feature, but it might be worthwhile playing around to see if you can as it could be that you can get 5 cores working fine without the increased power draw.