I am not an expert at this but if I recall correctly "Tallboy" was a 10,000 lbs bomb or something, the "Grand Slam", as its name reveals, the biggest (at least British) bomb with 20,000 lbs. I saw some impressive photos (in a book) of German sub-pens destroyed by Grand Slams in France. Several meters - seven meters I think - of reinforced concrete (with a lot of steel bars in it!) had been pierced, leaving a great big hole - direct hit. Or was it "only" a Tallboy? No, I think it was a GS.

I think the GS was the biggest bomb used during WW II, perhaps with the exception of the atomic devices and possibly the rotating ones used against the dams? No I don't think the latter were quite that heavy. Only a Lancaster was able to carry the Grand Slam (and take off with it!) in a modified bomb-bay. The B-29 could have done it too but it wasn't used in Europe, as you know.