I have found the KV-1 (not so much the KV-1s) to be very survivable when used in Heavy Tank Regiments, and capable of doing some damage to Axis armor. Even better, they are "free" (0 AP) support units that make a nice addition to Cavalry, Tank and Mech Corps with good Mech leaders. By mid-1943 you may be running short of enough T-34's to build brigades, much less regiments (and likely not enough T-70's to properly fill them out anyway), so why not take the free heavies?So as long as I can build T-34 equipped brigades that have more tanks with the same armor penetration values than a KV heavy regiment and can eventually become guards, that lead to corps, that is my priority.
All the above depends on how many Tank Corps you plan to build. Are you planning to build the Build Limit = 29, or some smaller number? I for one think Soviet Tank Corps are very weak until the 43b OOB appears in November 1943.