A good document for the T-34....it takes 13.8 seconds to do a full 360 deg turn of the turret
The following site gives details for the Sherman....
Medium Tank M4 Sherman , the turret traversing rate is 24 degrees per second, or slightly slower than the T-34/76, 14.4 secs
I dont know the exact traverse rate for the Mk-IV, but the wide tracks for the mkIV, the Ostkette were not available until the late summmer of 1944, and then only with a limited scale of issue. Most of the MkIVs career were fought with narrow tracks, so it is not incorrect the T-34 as having a decided mobility advantage over the MkIV