(1) - the B Concourse is only accessible via an underground walkway that goes from next to gate A1 (which is next to C28). Going from B to C means simply going through the tunnel and hanging a right. If it's a mid-to-low C gate, the tram will likely be faster (stops by C1 and C12).

(2) Tram is going to be faster to walk the entire length of the concourse. It's a good half-mile from C1 to C28, so unless you're a decent runner, the tram will be faster.