I'd fancy Lesnar against a few of those, too. I definitely think he could beat Travis Browne (which I'd love to see) and possibly Arlovski, depending on which version of Arlovski showed up. Barnett's catch wrestling and submissions could cause him a problem though, that would be an interesting fight to see.
I wouldn't fancy Lesnar against any of the top 5 (Werdum, Velasquez, Overeem, Dos Santos, Rothwell) or against Miocic, but it would be interesting to see how a healthy Lesnar would do against some of the others.