That's kinda impossible to tell because the Majin Boost, due to being more of a potential unlock, has different resutls depending on the fighter.
But assuming he got a boost comparable to Vegeta's (who got a ~1.25x one according to my estimations) then Cell Games Vegeta gets stomped, as I have him at ~60% of Cell Games SSJ Goku, the latter who should fall a little behind Dabura IMO.