Make a list of the fastest fighters at doubling shots in the HWs. Ali, Tyson and Lewis are the first who come in my mind. Which others in your opinion?
hand speed is a myth a lof of combos you see are a result of a guy in a high guard getting bombed on, positioning leads to good offense not hand speed.
Not Lewis, Tyson or Ali. The fastest combination punchers are smaller men. More than that, there are "combination punchers" and combination punchers. Naoyao Inoue is fast on a one-two, but he's throwing the sixth and seventh punch in the combination with as little gap between them as the first and second. This is something that heavyweights are absolutely awful at, because it's all about balance and small moves. Second, there is the question of power on the punches. Scoring combinations are fine but really long, really fast, really powerful combination punchers are so much rarer than people think (I think). Sugar Ray Robinson and Sugar Ray Leonard are absolutely comparable for fast combinations (balance, accuracy, timing, fluid mobility) but Robinson clearly outstrips him to my eye in terms of hitting very hard. Armstrong throws very many punches but doesn't reflect their excellence in accuracy and timing; Olivares is as good as anyone over four punches, but he trails off after that in terms of absolute excellence in these areas. I think the best I've ever seen in this department, I think, would be Ray Robinson, Manny Pacquiao and Roman Gonzalez. Now all you have to worry about is defence, positioning, shot selection, anticipation bleauch. Incidentally, I stopped following along and am kicking myself about it but I think that you can see Canelo improving in this regard in five-fight clutches. That is, you can see him getting better at staying fast-handed on longer combos. I kind of wrote him off (maybe unfairly) as a one-two merchant when I first saw him box and then he added a third good punch and a fourth. Worth thinking about if this is interesting to you.
Patterson was one of the fastest combo punches of all-time and the fastest combo puncher in heavyweight history.
People, this is just about HWs, and we only have a handful of fast ones: Tyson, Patterson, Ali, Louis, Dokes
As to the speed of his combos Lewis is very underrated above all here imo. He destroyed many opponents with photonic combos (Bruno, Ruddock, Golota, Rahman II and others).
Holyfield threw some snappy combinations. He would bring that left over/under. Faster then most heavyweights could. Evander still had the coordination and quickness of a light heavyweight.