I think it would depend on many factors - how proficient you are on your own DSM, the quilting pattern used, the size of the quilt, how tolerant you are of having to shift the quilt around on your DSM, if you can afford the rental fee. I have a Tiara - a sit-down machine. I can't imagine trying to quilt on a DSM after having the Tiara. The harps on most sit-down machines are huge and allow for much less shifting and struggling. I imagine it would be much faster.
However, another consideration is that the sit-down machines don't have feed dogs, so straight-line quilting needs to be done with a ruler. Stitch-in-the-ditch is also harder too, I find.
I think the only way to decide is to try it out once and see what you think. I imagine everyone would have a different answer.