Low to mid 40s is good enough for this, Mehring, I promise. And this reserve business winds up being a nice morale builder.
I only hesitate when the morale is absolutely craptastic. Defined for this purpose as sub 40 morale. Those guys...yeah, I have special missions for them in 1941. They go on suicide picket duty. If they die, great. I replace with them a cadre with much better morale. (Yes, it is actually faster in 1941 to build morale this way than to train units with especially bad morale.) If they don't die, also great. Keep sending them back out there until they do (at least until November, then you are stuck with training them.) Don't put these guys on refit, either. They can hug the Germans, put zocs on everybody, and cause them attrition losses.
Speaking from painful personal experience, this is a great thing to do as the Russians.
"We are going to attack all night, and attack tomorrow morning..... If we are not victorious, let no one come back alive!" -- Patton
The Logistics Phase is like Black Magic and Voodoo all rolled into one.