As @hexahedron mentioned, best guesses for “perfect” komi, for all board sizes, are:
- 6 for territory scoring
- 7 for area scoring
Convention in most rulesets is that ties go to white, so 6.5/7.5 it is. Ing SST rules dictate 8 komi with ties going to black (still 7.5). New Zealand rules allow draws and use 7 komi (maybe you’d like to try that out).
It seems like some people find 9x9 harder as black, others harder as white. At 6.5, it does favour white by half a point (whereas 5.5 favoured black). The in-development ratings system change will include komi in ratings update to model this (dis)advantage.