I've been trying to decide between roundwounds and flats on my fretless jazz. I've been switching between a set each of DR Highbeams and TI Jazz Flats. Problem is I love both sounds. I was wondering if the repeated tesioning on these strings is messing with the tone and shortening the life of the strings. The upside is I've gotten good at adjusting the saddle height and neck relief pretty quick.
I would say that the string fatigue has a lot to do with the quickened deadening of the strings. The stress done to the string every time you put it on the bass will certainly affect the string's integrity. As far as the strings go, I had the same problem you did--I love both the flatwound and roundwound sounds. I took the easy way out-I bought another bass.
bassmonkee's dead on, IME. Each time you restring, the string is not breaking at precisely the same point on your tuning pegs. Consequently, the inner windings decrease tension and your sound suffers. I did this many moons ago with Fender flats, and the outside wraps started unwinding on some strings, starting at the break point on the tuning pegs. Not a pretty picture and the outer wrap tension loosened along the length of the strings. With the roundwounds, you should be seeing indentations along the strings where they hit the fret wires when you restring. When these markings were aligned over the fret wires, they didn't affect string performance because they always made contact with the fret wire. When they are aligned over the frets, they don't make contact with anything and the strings may perform a little differently.
Round wound or flats on a fretless? shoot, if i had a fretless, id hit the flats.......SILKEY! hey, maybe i could make my P-Bass a fretless! ......ok,,,,,maybe not.....well.....wait....why not?
What about halfwounds? You get an in-between sound compromise. The life and lack of fingernoise of a flatwound with some brightness of a roundwound.