Gai wins
1tails Yugito was outmaneuvring B in CQC, someone who outmaneuvered Sasuke(albeit weakened)
V2 Sharinegan Jinchurikis > 1tails Yugito in CQC
6gated Gai was outmaneuvring multiple of them
So Sasuke doesn't stand a chance in close combat. Long range distance won't work either. Gai's movement speed in 6gate is so great that he almost caught off-guard a Kisame staying something like 50meters away from him in one jump, so he should be able to dodge his katon. Chidori nagashi or kawarimi seems to be his only best bet, but not only he'd have to be able to react in time, but kawarimi takes a lot of chakra from him out, so won't pay off in the long run
Sasuke isn't a summoning specialist. He only uses it either as a defensive shield or when he is in a mess and by the time he'd probably think about doing it, he could be finished by asakujaku. Either way, even if he does, he'd have to control Manda during the entire battle for him to cooperate and it doesn't seem like he could do it for long. Not to mention, Gai could ignore him and attack Sasuke directly
I'm not sure about 6gates Gai though since we've no idea concerning the power and speed boost he receives in the mode
