Just plain loud and loud in a group setting is a little different.
I can certainly understand how even Spirocore mitts would sound louder when simply playing. But I think the reason they are so loud is that they are a bit mid tone heavy. Mids are generally the key to the perception of loudness. They also allow the bass to cut through the mix. This is probably why jazz guys love them. The bass lines are clearly heard.
IME, Obligatos are also pretty loud, have enough midtone to still have life, but are a little tubbier and have more bottom end. I would prefer these characteristics if I was playing BG all the time, as it only takes a couple of D28s to generate a giant, impenetrable ball of mid that nothing will cut through.
Even one loud guitar chunking on the downbeat with the bass line will eat you up.
I like a little tub on the bottom where they can't go. Plus it is a little more in line with the traditional BG sound.
The ease of play of the Obligato is gravy. If you have no experience with spirocore, even mittels offer quite a workout. If you go with starks, well, let's just say they are stiffer than most strings you'll play.
The local shop I stop by once and while sets up all its basses with helicores. I've haven't played them for more than a few minutes at a time, but I'm guessing you'd get a pretty good sweat worked up with them as well.
