Actually, the official TDP for the Athlon II X4 631 part is the SAME AS THE A6 PART WITH A WORKING RADEON CHIP YET IT HAS THAT PART DISABLED. So in reality is probably much lower 100 Watts...
So you're going to be bound by the board clock and not the TDP of the processor.
I'm not sure I am understanding your point, so apologies in advance if I have misinterpreted you.
I don't know why you think the TDP of the processor won't be a problem. When you overclock significantly, it is assumed you will be exceeding the rated TDP of that processor. A 1055T, for example, is rated at 125W, similar to its bigger brothers (1090T and 100T). At stock, its "real" TDP is probably lower. It doesn't really matter, because what's important is the TDP sets the minimum required cooling that will be packaged with the chip, or, in an OEM build, packaged with the computer unit. So as long as the 1055T is rated at 125W, it will be packaged with the stock AMD heat-piped cooler (not the Athlon / Athlon II coolers that look like a bare aluminum block with fins and a fan).
This also helps the company bin more products successfully into the target model. If they made the TDP ratings much less loose, then it will affect their binning, because suddenly each 1055T (for example) will have to be "more perfect" (less leaky) so that it fits comfortably into the supposed 1055T TDP rating (let's say, 100W). You can see why this would give little benefit to the company, so they stick (wisely) to just sticking with similar TDPs to bigger groups or families of processors. This also lessens the validation process that OEMs need to do.
As for the Athlon X4 631, yes, it is rated at 100W TDP only to simplify the OEM validation (for their cooling - so that they need no other special validation for the 631 as opposed to the rest of Llano), so it would not be surprising to learn if it is true that most 631 chips have a far less demanding "real" TDP. And as already stated, this will also allow AMD lots of room to bin chips to this model - even the leakiest ones that cannot possibly be binned to any Fusion model can simply be binned as a 631, even if this particular leaky chip's TDP was measured to be 50% more than most chips binned as a 631, as long as it fits into the target 100W TDP.
Having said that, it makes no sense to assume that just because the "real" TDP of something is not approaching the rating, then the TDP will not be a problem when overclocking. We have no data on the power and thermal scaling that extra volts and/or significantly more clocks produce for these chips. It can also be variable, given that just because two chips come from the same model (or, to be more exact, "got binned" as the same model) doesn't mean they will end up having exactly the same characteristics (such as OC potential, "leakiness", specific tolerance to voltage, or even just plain lifespan).
So there is simply no guarantee that the TDP cap will not be a problem, as far as I can see. As long as we are applying more voltages and higher clocks, chips will routinely go over their rated TDP, which is why we end up having to use 3rd party coolers designed to handle much greater resulting TDP (and the highest-end air coolers are rated as high as 200W+)
TL;DR: Just because the 631
should have far lower TDP than most Fusion chips doesn't guarantee us that all we will ever need is a 100W TDP cap. I maintain that unless the Llano TDP cap becomes a setting in the BIOS that can be overridden by overclockers, Llano (although maybe not the 631 specifically, but the A8 is part of your links) will not be an overclocker's joy due to the hard TDP cap limiting your OC and making the GPU next to useless as the AnandTech OC attempt showed.
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