This covers a variety of ideal/aimed for Soviet advance rates, citing translated primary sources when possible. The actual ability to meet these rates in practice would depend greatly on circumstances. All figures are in kilometers per day.
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Late 1940-mid 1950s (conventional): 25-35 infantry, 40-50 tank armies [Front Offensive Operation, 1974]
Late 1950s (nuclear): 45-60 [Front Offensive Operation, 1974]
1960s (nuclear) 60-70 [Front Offensive Operation, 1974]
Late 1960s (conventional): 35-40 [Front Offensive Operation With Conventional Weapons, 1969]
1970s-80s (Europe): 40-60, 30 (Southwest Theater, Mountainous) [Voroshilov Lectures, Front Offensive Operation, 1977 , Heavy OPFOR Operational]
1970s-80s (China, other weaker opponent): 70-100 [Voroshilov Lectures]
1990s-2000s (conventional, GENFORCE-Mobile): 30-40 (optimistic), 20-30 (optimistic, poor terrain) 15-20 (modest) [Generic Enemy: Mobile Forces]
Fuldapocalypse Fiction 
We’ll never really know how accurate these would have been. I was going to say “a shame” but no, it’s better we don’t know.
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