He'd beat Lesnar.
Machida is like the terminator, super-saiyan version of Randy wrestling wise, and he's got the best striking at 205. Lyoto would stuff Lesnar's take-downs like Randy did except I think he'd finish Lesnar standing after a big hit.
Lyoto's TDD and wrestling negate his size disadvantage. Not saying he'd be in contention (JDS is a training partner/would kill him, Velasquez would terminate him etc) but I think he'd break top 10 without a lot of struggle.
sig credit to Limba