Have not waded through whole thread…if you dig rounds, then agree that DR Sunbeams or Smith Compressors are worth trying if you want the round wound zing and to minimize board wear.
BUT…my favorite strings of all time, on fretless, are the Sadowsky Flats. I have them on my fretless five, and every time I play this axe, I marvel at the tonal range I can pull out of these. Not as slappable as rounds, but that's not why you have a fretless in the first place! Otherwise, very sensitive to touch and right-hand placement, capable of blooming like an upright, or cutting like mad, with a bit of judicious eq or appropriate hand technique. My fretless has a single MM pickup, and if I pluck down by the bridge, with a mid-range bump, I can get a pick-like attack, that sounds like the 1980's. I've otherwise used DR (Like them also, but thumpier), different La Bellas, TI Jazz Flats, Chromes (do NOT dig them…)…the Sadowsky flats rule.