Slow decay and modern tone for more modern types of jazz is pretty standard. I think your leanings toward Spiros is probably a good thing. Old jazz and roots, maybe different depending on your tastes. Volume with the Slaps shouldn't be an issue if you're amping, but decay and tone probably would be.
Just keep in mind every DB responds in its own way to strings, including Spiros. Setup, including sound post positioning, can make a huge difference.
Regarding setup, you might want to check how much relief (scoop) has been provided in fingerboard dressing for the Slaps. If you have sufficient relief so the Slaps are not buzzing, it might be too much relief for Spiros which are generally thinner (especially with the higher strings) and higher tension. Too little relief for the strings in use can cause buzzing, too much relief for the strings in use can make the instrument difficult to play.
Strings can be a rabbit hole. Best of luck with your decisions.