Yeah, my understanding was the heating affected the battery. Steam torps wouldn't be affected by this process, not having a battery.
It looks like the stock behavior is that G7e torps not using the pre-heat ability go at their heated speed and when you use the pre-heat ability they go even faster

Of course the in-game TDC is hardcoded that T2 = X knots so the "supped up" torpedo is not traveling like TDC expects and more likely to miss.
As for the range difference... I don't know if SH5 considers torpedoes to have a max distance range or a max time duration.