It's been a while, but if I recall correctly, the 840T mostly have defective cores that were sent off to OEMs for budget builds rather than ones that were simply locked. You would need a very specific use case to really get much of a benefit from getting the 5th and 6th cores unlocked - the six-core Thubans just didn't perform that much better than the four-core Denebs and in gaming, the gain is just about nothing. The 960Ts, also an OEM CPU rather than one that had general release, tended to have far better odds of unlocking.