I've never used the Vulpine, but I also rec the Smallblock 8's. They are a pretty incredible tire...as long as it's dry. They get hella grip on dry rocks, dirt, roots, pavement...and they roll like a madd fool. Enter any moisture...and they are a bit squirrely.

The Kenda Slant Six is another interesting option. I can't vouch for it yet, but I'm probably gonna try them out.