Just put a set of the 55's on my 4-string G&L L-2000 Fretless. Not string-thru body, in-line tuners, and the thick part of the 115 E string does wind on the post about a 1/4 turn. Hopefully this won't be enough to break the core - but I'll report back if it does.
P.S. Had some trepidation about putting these SS roundwounds on a fretless that had only worn flatwounds, but I have a flatwound-strung P bass for my "round" sound and I need the L-2000 to be my "sharp" sound. I've heard that the DR steels are among the most fretless-friendly out there, and I hope that will be the case for me. I got a little alarmed when after only an hour's playing there was a little carbon-copy impression of the string (right down to the windings) on the ebony fingerboard - to my relief it came off with a polish cloth, but I'm going to keep an eye on this, and jump to nickel Sunbeams or GHS Brite-flats if I see undue wear (not looking to keep it pristine - this is a player).
But I'm LOVING the sound . . . gets that piano-timbre on the E, nice growly aggressive sound when you roll on the treble and/or engage the hi-boost pre, and cleans up nicely (though with still a "don't mess with me" edge) when you dial back or go passive. And even though they are thicker than the 45-105's I usually use, they are as flexible.