Just using some of my own data to extrapolate: I've played 9806 hands in 4255 minutes with a MT ratio of 1.67. So if we do (9806/4255/1.67)*60*3.5 we get 290 hands per hour, if the MT ratio is 3.5. I'm guessing there's some time in which 4 tablers have to find new and better tables, right?
Then 15 PTBB/290 hands = $x/100 hands we find a winrate of 5.17 PTBB/100 in order to make $60 per hour. I'm sure some 4 tablers would post their own data to find out how many hands you play per hour on 4 tables.

That seems very doable.