I built this analysis over more than 4.5 millions of game played in Chess960 variant: 
https://github.com/welyab/chess960-win-by-position-setup

The most unbalanced setup is RNBKRBQN where white has 51.44% of win, and black 44.75% of win.

At general, white has a win rate of 49.17%, and black with 47.1%. There are more information on gihub repository.