Its got to be closer to 70%. If you go all in, youre rarely going to have more than 1 caller.
If youre against something like KQ youre a huge favorite. Any other pair is 80% fav, so that has to compensate for the times you get all in against 2 hands and win only somewhere around 60%.

According to my poker simulator vs a random hand you are an 85% favorite vs 1 player, 73% vs 2 random hands, and 63% against 3 random hands. These are randomly genertated hands but the numbers are probably close, whjen you think about it in terms of real poker hands, the hands that somone is likely to go all in with prefop are often hands that AA really dominates, such as KK QQ JJ and AK.

Found this on a website a long time ago...

# Opponents- %Odds of winning

1- 85.3
2- 73.4
3- 63.9
4- 55.9
5- 49.2
6- 43.6
7- 38.8
8- 34.7
9- 31.1

Not sure if these are simulated results or not