I own a Fender Jazz and a MM StingRay. The Jazz is tuned Eb and is used in my cover group, and the Ray is tuned standard and is used in my tribute group.
The 5 would be used in my cover group and for any other time I need a low B. I personally am more of a passive guy, but I've been watching a lot of Marta Altesa's YouTube videos, and I love the tone of her Ray. That said, I also love the tone of my Jazz.
For what it's worth, most Fender 5-lovers seem to prefer the P over the J.
If you already dig MM, and can roll with the narrow string spacing on the MM 5-strings, then consider going there, then lose the 4-string MMSR. Two axes, covering a whole lot of territory. Wouldn't be the first time I've seen those two instruments in someone's bag or on-stage setup. Also echoing Post #20, to check the vitality of that MM G-string. For reasons I don't comprehend, some of them flat-out suck.