If you go through the tech tree and inspect the rate of fire on the IS-M's top gun, you will find 4,51.
However, if you go through tank compare, the gun has a fire rate of 5,35 on a stock configuration.
I just got the 705. It has the exact same gun, however irrelevant of the way you look at it, its firerate is 4,62. That is marginally better than the first listing of the IS-M, however much worse than the one listed in the second image.
With a rammer, 100% crew and BIA, I was able to get the reload time of my IS-M down to 9,8 seconds. The exact same configuration on the 705 gives me a firerate of 11,2.
Is this a glitch or am I missing something?