The white martians are very powerful beings.
While all martians have the same powers and abilities, the whites tended to focus on the physical attributes of martians, and the greens on the mental abilities. That's why J'onn's telepathic powers seemed powerful enough to withstand multiple assaults from the linked minds of several white martians.
It was said in their first battle with the JLA that "Away from fire they're as strong as superman is, as fast as he is, and as tough". I think they are quite close but not exactly(100-100) equal. However, they showed in that first encounter that they were immensely powerful, they moved what seemed to be mountains of topsoil, showed superspeed that was between Superman-Flash level and the kind of toughness that very few beings outside of superman would show.
Yeah, I know, they're not quite equal to supes. However, just as Draco69 said, their abilities seem to differ, so some may be a little stronger than average or faster than average in terms of Martian power. Zum showed insane speed(Flash had to enter the speed force and travel at lightspeed to outrun him) as well as super toughness when he took flash's infinite mass punch that sent him into orbit and then back to earth again but on the other side of the planet from where he got punched by Flash. They are also very ruthless, and seem to delight in torturing others. A major factor in this battle could be the impact of the hyperclan's linked telepathic minds.