At 150' you could probably go as high as a 12,000lb ball but you will have to be pretty close to your work. On a 60-65 tonner w/150' of boom you can work at a down angle of about 36 degrees and that will give you about 125 feet of radius but it will greatly reduce the load capacity. I have had a 200t Manitowoc raise off the ground being held by a strip pf caulk because we had to boom down so low to reach the 5000 lb load. For a good all around baller I would go with a 10000 lb ball (or a little less) so that you can boom up and down as needed to reach as much of your target as possible without having to move a lot. If you keep your boom angle above 45 degrees you shouldn't have too much trouble working five or six stories. Just remember that a truck crane is going to be more tippy than a crawler when balling. It doesn't mean its going to go over it'll just feel like it.
Good luck!

My last truck crane was a 1970's 70ton P&H and it served admirably so you are probably in the right ballpark weight wise, I would make sure that there is some good nonspin cable on the drums. Compare the drum brakes, I would go with the one with bigger brake surface (helps not loosing the ball if you're balling).
How new are the ones you are looking at?