On the one hand Starks later model armours should have better feats than Mac's suit.
On the other Mac still has the best feats of cybernetic link/technopathy. While they've both cybernetically linked and hacked alien systems Mac has done it a lot faster.
If Mac goes straight for the hack to undermine Stark's armour he ca take it. In a straight up fight (which is more how I see it playing out) Stark should win