I see the stand up as fairly even in some ways, Mir's more technical with less power and Roy has more power and a rock solid chin. Mir has never had consistent solid TDD in the past, Nelson should be able to work a takedown at some point but whats bigger IMO is that Mir should have a very hard time taking Roy down.
To me Mir's chin makes this fight swing in Roy's favor. I can see Mir with a slight edge in the first round but I think somewhere during the last two rounds Roy will catch him with the same big shots he did JDS except Mir is half the boxer JDS is and Roy is going to catch Mir with more shots than he did JDS and at some point put him out.
TBH I hope somehow it goes to the ground because I dont care who wins and I want to see some high level BJJ from both guys.