Heat difference between 965 c2 and 1055T

I currently have one of the original 965s - the 140TDW version.

If I swapped to the 1055 6 core CPU, with a TDW of 125, would I notice much of a difference in temps?

Logically I think I would, but just want to be sure before considering a change...

Not really. they are the same architecture but +2core.
Temps should be below 30c with stock cooler.

If you were to look at the power usage, yes, but it really does depend on how good your cooling setup is. You'd probably see a 5-10 C, but I'm not sure.

So in theory the 140 -> 125 tdw will drop temps by a possible 5-10c?

Well thats a good reason in itself to upgrade I suppose?

I honestly do not think you will see much difference.

Expect to get 6 cores in the same power and thermal envelopes as the older 4.
The new cores are better at power efficiency and you still have a big pile of cache on die that accounts for big chunk of the power consumption. In some cases with 6 cores running you may find it pushing the envelopes a little. It all depends on how efficiently the code running on it keeps the cores banging numbers. Some of the distributed apps have been known the get 90+% true utilization and have been know to take down an otherwise stable rig.