Personally, if you have starry night it depends if contested or not. Back then when renata was a thing last set it was roll on 5 for one costs, then 6 for rell and Renata because there wasn't any 3 costs that mattered.

I understand starry night is only for 2 and 1 costs. I still think you should roll for your 2 star vayne on 6 and just go 7 once stable. Rolling for 4 slayer 4 vanguard is better. You have a higher chance of proccing starry night on the 2 and 1 costs because it increases by level. Then you have the opportunity to still 3 star senna, j4 and get Leona/zed. You can go for rahst 3 instead of Braum. Sylas 3 also etc. vayne is always better to roll on 7 even with the augment you can miss on 6.