I dont know why you say "Race lines".
Well, I do, as you mean "Thin" lines.
As race lines need to be able to withstand even more load than most other lines, so usually not superthin.
I think it matters at the ultimate low end especially.
Use 0,83 mm frontlines and 0,6 mm rearlines myself sometimes, when at the utmost low end.
Think the difference is mostly mentally though, but it matters too, and just the thought of the little gain it delivers, is sweet of course
Only thing is, some superthin lines tends to "howl", the faster you go the louder