I haven't tried Circle Ks yet but I've tried an SIT .165. The string itself seemed good but unfortunately it had a long length of exposed core. With my typical top loading bridge this left over an inch of exposed core in the vibrating length, this gave the string a strange 'hollow' / 'out of tune with itself' tone.
Obviously, the less a string is full gauge from bridge to nut, the less it vibrates like a non-tapered string. Having a significant part of it's length tapered or exposed core creates this inharmonic tone. It's essential to minimise the length of the tapered section, but many manufacturers tend to make it fairly long to fit a wide variety of bridges.
Also, the thinner the tapered section is, the greater the effect. Exposed core seems to suffer from this problem more than taperwound with one wrap layer over the saddle. So I now avoid exposed core.
Circle Ks have a well designed taperwound section of only 1.625" in length. On a typical top loading bridge this leaves roughly only 0.5" in the vibrating length.
Circle Ks are nickelplated steel outer wrap on steel inner wraps, should be smoother for your fretless board.
Traditional tension sets are only available for up to 6 strings, so you have no choice. Balanced tension is better for ERB and chording because the high strings are not tighter than the low strings. The balanced sets have roughly equal tension on each string, so the subcontra strings are not floppy.
If you like your strings loose, I would suggest a set with a .100 E. Remember to order a 'standard balanced' set for a 34" / 35" scale.
These are your set choices, assuming a 34" / 35" scale:
Circle K Strings - Standard Balanced 9 Strings
The sets with a .100 E have .136 for B, .182 for F# and .244 for C#.
