Correct me if i'm wrong:
Stug 3 + Tier 1 and 3 buildings + teching cost: 180 fuel
+10 Tier 1 building
+25 Battle phase 1
+35 Battle phase 2
+35 Tier 3 building
+95 Stug 3
-20 starting fuel
T70 + Molotov + Tier 1 and 3 buildings: 160 fuel
+25 Molotov
+40 Tier 1 building
+90 Tier 3 building
+55 T70
-50 starting fuel
These numbers only work under the assumption of equal map control. 5 Conscripts with molotovs WILL hold more map than anything the ostheer T1 can provide. The Stug comes several minutes to late, in which you most likely will lose total map control. Plus, the Soviets have more manpower to spend until both units hit the field.
Even a fuel cache won't make a difference, because +3 fuel equals one normal territory point (which you most certainly won't posses at that point).
Oh dear, it seems that I have been spewing nonsense in some threads! I was under the impression that german battlephase 1 was 15 fuel instead of 25. The T3 building is 25 rather than 35 fuel though, so in the end the soviets can get the T70 for 10 fuel cheaper than a german can get a STUGIII. For the same price if they go for T2 rather than T1.