When I used to fly the polar routes from DTW to HKG, the company would send a sample of our fuel to a lab to determine the actual fuel freeze point for that particular fuel load.
We usually got the results via ACARS within an hour or so of departure and would then enter the actual fuel freeze temperature into the FMS in order to overwrite the default value.
I don't recall ever having to speed up or change altitude due to fuel temperature issues, but I may have just been lucky.