Sabo (premera mera) vs. Ace - Sabo (Mid-High diff)
This is because, Sabo and Ace were portrayed equal in strength since the very beginning and Sabo became a known revolutionary without depending on a DF which pretty much makes me believe that he is a Haki beast. Secondly, the way sabo toyed with both burgess and diamante to get the mera mera no mi is astounding and this is post-skip burgess we are talking about here.
Sabo(mera mera) vs. Vista - Sabo (Mid-diff)
I personally think talking about vista holding his own against mihawk is bad example. Because even crocodile did the same for a degree and so did Jinbei against Mihawk. Also a point should be noted that, Mihawk kept his "Hawk eyes" on Luffy the whole time he was fighting vista, so it's not like Mihawk was being serious.
And Vista vs Mihawk was just like Sabo vs Fujitora (It all happened off-panel) and what we saw is both quitting the fight with mutual agreement.
Sabo (mera mera) vs. Jozu - (not sure at all)
I am not so sure about this fight, Jozu has a hax DF, the question is can the diamond stand against Haki? Can that diamond be coated with Haki?
Sabo (mera mera) vs. Marco - (I would say sabo but it could go either way)
Marco has not displayed any great Haki feats in the war. He sent Kizaru flying, but Kizaru keeps trolling ON and OFF.
But I feel pre-skip sabo would have won High diff. Post skip Marco would mid-diff sabo.