Vernon Davis is 6'3", 250 pounds and runs a 4.38 40 yard dash. Vernon Davis is a second faster than Victor Cruz. The Giants defensive backs have some decent speed: Corey Webster: 4.5, Aaron Ross: 4.41, Antrel Rolle: 4.48, Prince Amukamara ran a 4.43 at the combine, but squeaked out a 4.38 on his proday. Matching up with Davis's speed is going to be an issue, bumping Davis in the first 5 yards will be crucial. The Giants have been great at defending Tight Ends the last 4 weeks, Chase Blackburn has been a key factor in the middle, but don't expect Blackburn (4.69) to run with Davis.
Against the Saints Davis benefited from some inside out technique by 2 DB's, Davis's speed means he can run by 2 DB's playing inside out. Downfield, bracketing Davis with 2 players is vital in making sure DAvis gets tackled after he makes his catch.
On shorter timing routes Davis may see a variety of double teams. The Giants covered these routes well in the Green Bay game and Perry Fewells schemes have done well in defending the middle the last 4 games.
Look to see Blackburn bump Davis and cover a crossing route in an underneath zone, with help from from a safety, as Davis runs thru the zone, Blackburn might hand off Davis to the next player in the zone. The Giants have been doing this well since Blackburns return, they've also down it with man and zone in the back end. Then to mix things up rookie safety Tyler Sash will play on run downs, he's a good box type safety who has a nose for the ball, 13 picks and 13 pass defenses in college.
The Giants defense is going to have to play lights out to slow down Vernon Davis, I can see Fewell mixing things up to keep Davis under control and it means QB Alex Smith will have to avoid the rush while deciphering the varying defensive schemes.