Brooke, it varies with different aircraft, but as a general rule both the tactical and limiting Mach speeds are below critical Mach. This was certainly true with the 109 because of the heavy stick forces at high speed. The P-38 was a special bird because of all the interference drag and Bernoulli effects created by the central pod and nacelles interacting with the airflow. Brown defines tactical Mach as the speed at which you can fight the aircraft and limiting Mach as the speed where you no longer can, and if you go past the limiting Mach speed you'll get into serious trouble.
The RAE extensively tested both the Typhoon and Tempest and they too had both tactical and limiting Mach speeds well below critical Mach. I quote from Brown's book Testing for Combat:
"Our other great interest in the Tempest V at the RAE was in its high Mach number characteristics, and these proved to be very similar to those of the Typhoon, except that it had limiting Mach number of 0.81 true and a critical Mach number of 0.83 true. At the latter speed the nose-down trim change was very strong, and a full-blooded pull was required to keep the dive angle constant until the altitude had fallen to about 15,000 ft, when recovery could be affected."
"We had found out that the Bf 109 and the Fw 190 could fight up to a Mach of 0.75, three-quarters the speed of sound. We checked the Lightning and it couldn't fly in combat faster than 0.68. So it was useless. We told Doolittle that all it was good for was photo-reconnaissance and had to be withdrawn from escort duties. And the funny thing is that the Americans had great difficulty understanding this because the Lightning had the two top aces in the Far East."
There, from the man himself.
The difference between the 109 and P-38 is that in the case of the 38 the tactical Mach speed is limited by compressibility effects, while for the 109 it is the heavy controls that limit its ability to fight above Mach .75. It doesn't get into compressibility until .80 or thereabouts.
