I think The biggest time gap made up is likely to be Fangio at the ‘ring.
In lap terms, it’s worth mentioning Jim Clark at Monza in ’67. In the 60s, Monza was the ultimate slipstreamer race – if you got spat out of the pack, you were considered to have no hope.
Clark lost a lap because of a puncture and came out in 15th, but he managed to get the whole lap back (through pure speed no some yellow flag), overtake *everyone*, and take the lead. The best victory in F1 ever was spoiled when he ran out of fuel.