Kabuto wins in the first scenario since minato doesnt have FTG so lets move on frmo this one
second scenario
with FTG kabuto will have a little more trouble..
thanks to FTG minato will be able to avoid kabuto's techs more easily and anything that kabuto throws at minato can be redirected thanks for FTG however this wont be enough to beat Kabuto..
Sage mode gives minato a nice power up but as others have said thanks to kabuto's liquifiing ability it doesnt help against him.. however the increased durability will be of help atleast here and use of nature energy and Kabuto will need to solidify again to attack Minato, Minato can exploit this, especially if he manages to place a seal on Kabuto.. we have seen Minato's reactions are one of the fastest.. if not the fastest in the manga so i can see Minato being able to exploit this weakness
this is more speculation on my part but.. since minato has sage mode.. he would of had to have trained for it since you need to train to be able to control and learn how to feel nature energy.. now the final part of the training is fusing with ma and pa.. so i would assume minato has access to them.. now if he does then frog sound genjutsu could be the deciding factor for minato to win..
but again as i said this is merely speculation and we cant really tell..
il just put it this way.. without frog song Kabuto would win high diff
If minato did have access to frog song then this could be the factor that allows minato to beat Kabuto.. again it would be High diff
its situations like these where i wish kishi elabourated more on Minato's sealing capabilities because this is where a lot of his power could come from and could have been a nice alternative than giving him sage mode but whatever
conclusion:
Scenario 1 - Kabuto
Scenario 2 - Kabuto - without frog song - high diff - this match could go either way still
- with Frog song it could go either way still but i would see Minato winning high dif