Wow, that's a tough one. Bernina is generally known as a tough machine, and I wouldn't worry about it not handling the quilting. What is the throat space on the Bernina? The bigger the throat space, the easier the quilting because you have to manhandle less bulk through a narrow space. I just bought a HQ Sweet 16 to do my FMQ because the Pfaff Grandquilter (the equivalent of the Brother 1500) did not provide me with adequate space.
The Brother is a straight-stitch machine and it sews very fast. If you wanted to set it up for just your quilting then you wouldn't have to change the settings on the Bernina from piecing.
Knowing now what I didn't know then, I would not buy the Pfaff. I would continue to use the DSM and save my money for a dedicated sit-down quilting machine. Good luck and have fun with your decision.