Not everyone is buying crossovers these days, some still prefer the classic four-door sedan. Mazda has freshened the Mazda6 for 2018 to do battle with Camry, Accord, Altima, Malibu, Sonata and Optima to name a few competitors. Tom Voelk checks out the new top-tier Signature model to see if it still has zoom-zoom chops and how it stacks up against all of the other offerings.