Pershing with it's wind-up has a much slower rate of fire than the Panther.
That is false, it does not have a much slower rate of fire. They have basically the same ROF. Both have 1s wind down. The average reload is 6.65s for the Panther and 6.75s for the Pershing. Both around 5s with vet 3, probably in favour of Pershing now that it gets -35% reload. The Panther has a variable reload value of 5.2-5.6s though, where the Pershing has a standard 5.5s, so occasionally it might fire ~0.3s faster and sometimes ~0.1s slower.
https://coh2.serealia.ca
And the Pershing can get an additional -30% reload speed for 45s with CA, while only the OKW Panther can get -25% reload for 10s with Combat Blitz.