Pe-8 was not a kind of UFO object, of course But you are right, civilians of GB and US saw the large Soviet aircraft which made long-range flights despite the German propaganda about total destruction of Red Air Forces and that was a good diplomatical step and small help to increase the unification of Allies in their efforts against Nazis.Oh. It was that good ?? People in GB and US seeing something with red stars, propably first time in their lives, and becoming interested
TB-7/Pe-8 was the one of best heavy bomber for 1941 (I don't write the best one especially ; the only full superior was more modern B-29) and British/US pilots asked to show them the aircraft with great interest to compare it with their own "Lancasters", "Liberators" and "Flying Fortresses" during the landings of Pusep's bomber on airfields. And they always said: "Ok..very well...excellent aircraft..." (see the memoires of Pusep and other crewmembres, for example). The only main problem of Pe-8 was engines (different "raw" models of engines were used because of need of good AM-35A engines for MiG-3 and Il-2), that is why only Pe-8 with AM-35A engines was chosen for that important flight. Also habitability was on low level than of more comfortable Allied bombers (Soviet engineers developed excellent vehicles but seldom thought about crewmembers to decrease the cost of vehicles, the comfort had insufficient importance for Soviets) - Soviet long-range bomber pilots, who used several B-17s in 1945 mentioned easy control of Boeing during the flight (but worser control duting take-offs) and high level of comfort (good airtightness - Soviet pilots of Pe-8 were used to be at -50, drafts and snow/water inside the cabin at high speeds; toilet - Soviet pilots of Pe-8 used cans for that purpose), but observability for the 1st pilot of Pe-8 was better. The quality of Pe-8 was very good because of its low serial production and strict control (that was almost "handmade" aircraft also taking into consideration its technology of production), early ANT-42/TB-7 of 1938-1941 had even much better quality than Pe-8 of 1941-1944. It represented a great step forward in comparison with obsolete TB-3, having all-metal construction from different and rear composites (some were used for the first time in aircraft industry), excellent aerodynamics (cx = 0,027) and flight specifications for large 4-engine aircraft, modern equipment (hydroautopilot, fixed loop radio compass, two powerful radiostations with different antennas including long retractable one, quite good night bombing site, wing ice-protection system, fire protection system for each engine, hydraulic/electric drives, etc.) - UK/US specialists examined the bomber with great interest indeed (that doesn't mean that Allied specialists found something completely new for them, but they found the excellent level of Soviet aircraft industry).
Pusep wrote that he was afraid that some of Allied specialists could note the holes from German AA shells in the wings (just several days before that flight to Washington Pusep's bomber participated in dangerous air raid, and holes were patched up carefully but still visible - but his navigator said: "if our foreign friends saw the remains of combat damages - that will be even better, we show them that we are the bomber not just private airplane for important persons"), also Pusep wrote that he felt inconvenience during the landing on Washington's airfield and their greeting of honor by US people as all wings were covered by oil from overheating engines because of maximal speed during the last hours of flight (interesting info according to Pusep's navigator memoires - Canadians sent B-17 to escort Pe-8 from Montreal to Washington, but Boeing got behind soon and lost the Soviet bomber).
http://www.23ag.ru/assets/images/VVS_3_7.jpg (US pilots looked upon Pe-8, Washington, 1942)
PS. I found some additional info about use of FAB-5000 super-heavy bomb - 1) the explosion during its first test (the bomb was dropped from 2.5 km altitude over the large forest) caused the fall of 600 trees (diameter more than 20 cm was taken into consideration only); 2) the explosion at Orel railway station before Battle of Kursk caused completely destruction of all buildings and railing 250 m around, platforms with new "Tigers" on board flied around; 3) after drop of FAB-5000 over Königsberg Hitler made an official claim to his generals next day that he allow to use chemical weapon if Soviets do this ones more.