When I first played my '77 MSB it had very old GHS 105-45 Boomers on it, and it sounded really good with that set. So I kept on using Boomers up until the first of this year, and then starting using Swing Bass steels; as they're easier to get around on and they're on many of my basses. There was something missing in my tone when hearing my Series 1 within the track after switching to Swing Bass, even though I could muscle them easier than the Boomers. The Boomers excite the magnetic field of the pickups more than most other steel strings, and definitely produce a bigger, beefier sound. They are louder than Swing Bass steel when compared directly.
I also hear a lot more beef in the mids, too, and this is why they speak so well in the mix. There's more of everything, except the highs are less prominent. They aren't as flexible as Swing Bass, but I can live with that. I guess I'm back using Boomers.