Typical high speed tracks aren't shared with cargo trains. Frankfurt-Siegburg for example is only usable by high speed passenger trains.
And regarding the max speed, I'd suggest to look at china. The chinese railways run the Siemens Velaro CN, which is the local version of the Velaro D (DB Br407) at 380km/h in regular use.
"at those temperatures"
well, to a heat pump even -40° is still 230K, which is plenty of energy to move around and work with. It may be cold to you, but to a heat pump it's not.