Before you laugh, remember, Stewart gave prime Holyfield 2 tough fights. He beat up George Foreman and left his face a mess. He would have a significant size advantage over Patterson.
Whenever Alex Stewart stepped up he was usually knocked out. The exception being that he went a full 10 with Foreman and busted him up pretty good. Foreman is not Patterson, and in this exercise I'm assuming both fighters are in their primes. Stewart could obviously knock down Patterson - lots of folks did - but I do think Patterson would be a pretty solid favorite here. Stewart is 20-30 pounds more than most fighters Patterson fought though.
Against a guy that can hit like Stewart its a risky fight for Floyd, but I do see him winning by decision.
Patterson by stoppage Stewart may floor Patterson and have a few moments here and there but the gulf in class between the two is alot....... Despite Stewart having a high KO ratio and having some respectable losses against some notable names. The fact is he never stopped any notable names nor did he beat any ranked Heavyweight. PS I just had a look at Stewart's record the best fighter he stopped was Ezra Sellers who was a Cruiserweight to my knowledge.