I can tell you my experiences. I had labella black on a 35" 5 string. I did not widen the nut, but it's possible I should have. It was looked over by a luthier, who fixed a few frets for me, and he liked the strings too. So for that one I didn't. But I bought it used with rounds on it, but it could have been widened before. That bass sounded excellent, but it was too heavy so I sold it. I put a set of white tapes on my daughters p bass, but this time bought light gauge so I wouldn't have to worry about the nut. It sounds great, but the tension is pretty low and takes some getting used to. At the time I emailed labella, and I got this order for brightness
from labella in my email:
760N - Black Tape (mellowest)
760C - Copper White
760T - White Tape (brightest)
I'm not sure where the 760G (Gold white) land except for brighter than the coppers. The 760G were not mentioned in my email. I'm not sure how they compare to the 760T. The customer service rep did say that the difference in tone between the 3 flavors of white tape (760C, 760T, 760G) was "subtle." The whites on my daughter's bass sound a lot like roundwounds to me - but without the finger noise. I like a little more mellow, so my taste is probably either the 760N or 760C.
As for the nut and gauges.... that's more a physics thing. The differences in attributes between light gauge and heavy gauge are similar to other strings. I'd recommend getting the regular gauge, and if you like them, have your nut filed if you are out of tune (should show up sharp in the first couple frets if nut is too high). If you like the strings you will likely keep them for years. They don't really seem to wear.
Also, you may need to pay close attention when looking at brands. La Bella's tapes are roundwound with nylon tape wrapping. I cant recall which brand, but one of them uses flats for the E and A strings, and rounds for the D, G strings under the nylon. Some people claim to be able to hear that. I haven't used that brand, so I'm not sure. I can say that a flatwound string with nylon over it will be quite a bit more mellow than a roundwound string with nylon over it.
Hope this helps. I'm trying not to color anything with my opinion, as my ears may be different.
@LowEndLobster threw some 760N black tapes on an AFR Affirma and gave me permanent GAS for that bass. He compares the black tapes to rounds I believe in that video. I will say, the Rob Allen fretless basses use Labella Black Tapes as their stock string. That is an awesome boutique bass.