depends on how much you think dd's own strength increased over the course of the battle. if he starts off facing the hooded dd that wasn't able to harm superman with a punch, that is different from the version that increased dramatically in power as the fight went on. the belt also doesn't increase his speed. that said, i think regular thor is capable of beating dos, so this one certainly could as well. i still don't think it would be easy, nor do i think strength would necessarily be the deciding factor--the hammer's versatility is still the key here.
Doomsday wins a majority in a conventional fight. He's durable enough and fast enough to keep evolving over the course of the fight. Chronologically, Doomsday has already killed Master Mayhem, Radiant, and thousands of Green Lanterns by the time DOS happens.
Thor has to use his smarts if he's going to beat Doomsday. Mjolnir can open gateways to really nasty places. Maybe a dimension that's equivalent to the end of time like Limbo would be a bad rabbit hole for Doomsday to fall into. Not easy though.