GrauGeist
Generalfeldmarschall zur Luftschiff Abteilung
Yes, they had manufactured 93 airframes (including the early TB-7 designation) and they had less than a great performance record.Below is from the Pe 8 article in wiki, Its strategic raid on Berlin 4 reached Berlin and only two returned, this was a symbolic gesture which almost certainly cost more in terms of Russian men and machines than German. Only 93 Pe 8s were built and front line strength was rarely above 20 from what I can see.
On the evening of 10 August, eight M-40-engined Pe-8s of the 432nd TBAP, accompanied by Yermolaev Yer-2s of the 420th Long-Range Bomber Aviation Regiment (DBAP), attempted to bomb Berlin from Pushkino Airfield near Leningrad. One heavily loaded Pe-8 crashed immediately upon take off, after it lost an engine. Only four managed to reach Berlin, or its outskirts, and of those, only two returned to their base. The others landed elsewhere or crash-landed in Finland and Estonia. The aircraft of the commander of the 81st Long-Range Bomber Division, Combrig Mikhail Vodopianov, to which both regiments belonged, was attacked mistakenly by Polikarpov I-16s from Soviet Naval Aviation over the Baltic Sea and lost an engine; later, before he could reach Berlin, German flak punctured a fuel tank. He crash-landed his aircraft in southern Estonia.[20] Five more Pe-8s were lost during the operation, largely due to the unreliability of the M-40s.[21] Seven Pe-8s were lost during the month of August alone, rendering the regiment ineffective.
But the point is, that the Soviets were striking Berlin (and other key targets) well within German proper from the early stages of the war. Along with the Pe-8, there was also the DB-3 (including the Torpedo carrying version, dropping conventional ordnance), IL-4, Yer-2, etc.
Their lessons learned in daylight attacks over Germany were comparable to what Bomber Command and the U.S. learned during the early days and their losses were comparable, percentage-wise.