For reference:
DK Jr took about 50 games to break 1m and DK3 took 3 games to break 1m.
With DK being the toughest of the 3 by far, 200 is not a bad starting estimate.
Well you should note that the DK3 is on easy settings.
Also, one more thing. All DK 1 million point games are not the same, even on correct settings. Since I am actually good at Donkey Kong Junior, and Donkey Kong 3, I know approximately what scores are equivalent to a million point Donkey Kong game.
Here is what I believe is equivalent to 1 million on Donkey Kong for both games
1.2 million on Donkey Kong Junior
4 million on Donkey Kong 3 Twin Galaxies Marathon settings
1 million on Donkey Kong 3 Twin Galaxies 5 man settings
10 million on Donkey Kong 3 Twin Galaxies easy settings