Robin's stronger than Brook or Franky pretty solidly, just too cheap. Notice how against the leader of Enel's militia she was handicapped and still won (or in other words, Robin is still in the "she faces a handicap in 1-on-1 fights" thing like Zoro and Luffy started out), or how at the buster call she was talking out more officers than the others.
Brook'd just get disarmed and trapped, he's really ill-suited to her. And Franky? We know how that goes.
In a rumble scenario I see Robin taking out the fodder pirates or marines instead of the more powerful ones...
Remember when she snapped Aokiji and Moria in half? Effortlessly took out a zoan fruit warrior? Sure, she's great at crowd control, but she can do stuff like form giant combined arms for extra damage now too.
I think both Robin and Sanji should be in the 100k plus range, and I'm not entirely sure which should be higher in fighting ability (Robin's more flexible and cheaper, Sanji can hit hard with less set up and has his flame leg thing too).
The crew has four monsters when it comes to power, with Frank and Brook being mid-level.