How much slower does diesel burn than gasoline?
There is no such thing. Flame speed depends on a huge number of factors such as air temperature, injection pressure, injection type (direct/indirect/port injection, number of nozzle holes), cylinder pressure, atomization quality, combustion chamber shape, moisture, EGR percentage, pilot injection, and on and on and on.
This is why a light-duty automotive IDI diesel can rev upwards of 5000rpm while the same bore/stroke DI diesel tops out around 4500rpm.
What are the main changes to the formulation of diesel in the last 10 years that make it flow better in the winter?
Irrelevant to the topic.
Why doesn't carbon damage soft bearing surfaces, but still damages hardened fuel system components?
Bearings have oil clearance (0.0022 range). Injection parts are mated machined surfaces (+/- 0.0002 machining tolerance).